V

THE

VOYAGE OF H.M.S. CHALLENGER.

ZOOLOGY-VOL. XXIII.

REPORT

ON THE

SCIENTIFIC RESULTS

OF THE

VOYAGE OF H.M.S. CHALLENGER

DURING THE YEARS i 8 7 3-7 6

UNDER THE COMMAND OF

Captain GEORGE S. NARES, R.N., F.R.S.

AND THE LATE

Captain FRANK TOURLE THOMSON, R.N.

PREPARED UNDER THE SUPERINTENDENCE OF

THE LATE

Sir C. WYVILLE THOMSON, Knt., F.R.S., &c.

KEG1US PROFESSOR OF NATURAL HISTORY IN THE UNIVERSITY OF EDINBURGH DIRECTOR OF THE CIVILIAN SCIENTIFIC STAFF ON BOARD

AND NOW OF

JOHN MURRAY

ONE OF THE NATURALISTS OF THE EXPEDITION

Zoology Vol. XXIII.

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CONTENTS.

I. Report on the Rteropoda collected by H.M.S. Challenger during the years 1873-1876. Part II. The Thecosomata.

By Paul Pelseneer, D.Sc. (Brussels).

( The Manuscript was received 2nd August 1887.)

II. Report on the Pteropoda collected by H.M.S. Challenger during the years

1873-1876. Part III. Anatomy.

By Paul Pelseneer, D.Sc. (Brussels).

( The Manuscript was received 5th December 1887.)

HI. Report on the Hydroida dredged by H.M.S. Challenger during the years 1873-1876. Part II. The Tubularhsle, Corymorphhsle, Campanularhsle, SERTULARiNiE, and Thalamophora.

By Professor G. J. Allman, M.D., LL.D., F.R.C.S.I., F.R.SS. L. & E., M.R.I.A., C.M.Z.S., Mem. Roy. Danish Acad. Sci., &c.

( The Manuscript ivas received in Instalments between 29 th August 1887

and 9th February 1888.)

XY. Report on the Entozoa collected by H.M.S. Challenger during the years

1873-1876.

By Dr. 0. von Linstow of Gottingen.

( The Manuscript was received 2kth October 1887.)

y Report on the IIeteropoda collected by H.M.S. Challenger during the years

1873-1876.

By Edgar A. Smith, F.Z.S., Assistant in the Zoological Department of

the British Museum.

( The Manuscript was received 21 st January 1888.)

ERRATA IN PART LJV.

Page 107, line 9, for globulosa” read gibbosa Page 112, line 18, add “Cuvierina columella.”

ERRATUM IN PART LXVI.

Page 2, line 23, for “Opisthobranchiate” read “Tectibranchiate,” and vice versd.

EDITORIAL NOTES.

This Volume contains Parts LXV., LXVI., LXX., LXXI., and LXXII. of the Zoological Series of Reports.

Part LXV. The First Part of the Report on the Pteropoda, by Dr. Paul Pelseneer, treating of the Gymnosomata, was published in 1887 in Volume XIX., and forms Part LVIII. of the Zoological Series of Reports.

This Second Part of the Report, by the same author, deals with the Thecosomata, and contains 132 pages of letterpress and 2 plates, in addition to woodcuts.

Part LXVI. In this Third and concluding Part of the Report on the Pteropoda, Dr. Pelseneer treats of the Anatomy of the whole group and discusses the relations of the Pteropoda to the other Mollusca. The Part consists of 97 pages of letterpress and 5 lithographic plates, in addition to other illustrations in the text.

Part LXX. The First Part of the Report on the Hydroida collected during the Expedition, by Professor S. J. Allman, F.R.S., was published in 1883 in Volume VII., forming Part XX. of the Zoological Series of Reports ; it treated of the Plumularid,® (Plumularinse).

The present Memoir is the Second and concluding Part of Professor Allman’s Report, and treats of the remaining families of the order.

In consequence of the extent and representative character of the collec- tions Professor Allman has been able to give, in addition to the zoological

mu

THE VOYAGE OF H.M.S. CHALLENGER.

descriptions, a very valuable and comprehensive sketch of the morphology and life-history of these animals. This Part consists of 160 pages of letter- press, 39 plates and a map.

Part LXXI. Had any special attention been paid to collecting Entozoa during the Expedition, a much larger number of species would probably have been obtained than are described in this short but valuable Eeport by Dr. 0. von Linstow of Gottingen, one of the first authorities on this group of animals. The Report consists of 18 pages of letterpress, 2 lithographic plates and a woodcut.

Part LXXII. In this Report Mr. Edgar A. Smith has brought together systematic lists showing the present state of our knowledge of the Hetero- poda, founded on the collections made during the Expedition. The Report, which consists of 56 pages and 5 woodcuts, will be most useful to future investigators.

John Murray.

Challenger Office, 32 Queen Street, Edinburgh, 9th May 1888.

THE

VOYAGE OP H.M.S. CHALLENGER.

ZOOLOGY.

REPORT on the Pteropoda collected by H.M.S. Challenger during the Years 1873-76. By Paul Pelseneer, D.Sc. (Brussels).

K'a.c/ x\

PART H.-The THECOSOMATA.

INTRODUCTION.

About the end of the year 1885 I was entrusted with the task of making a systematic and descriptive Report on the Gymnosomatous Pteropods and an anatomical one on the entire order, and in the beginning of the present year (1887) the entire Report on the Pteropods was entrusted to me for completion.

The Report is thus divided into three portions as follows :

1. The systematic survey of the Gymnosomata, which has been already published.1

2. The present Report on the Thecosomata, which along with the former includes the entire systematic survey of the Pteropods collected on the Challenger Expedition.

3. The anatomy of the Thecosomata and Gymnosomata.

As with the Gymnosomata, so in regard to the Thecosomata, I have been forced to make a monographic study of the entire subgroup. But I have not here described all the species actually known, partly because they are on the whole more familiar than the Gymnosomata, and partly because the delay which has been involved in the completion of the entire Report made such a survey impossible. I shall therefore restrict myself to an enumeration of the indubitably genuine species among the entire list of those hitherto described, and to synoptic tables in which these are distinguished from one another.

1 Zool. Chall. Exp., part lviii.

(ZOOL. CHALL. EXP. PART LXV. 1887.)

Ttt 1

2

THE VOYAGE OE H.M.S. CHALLENGER.

And as to the species collected on the Challenger Expedition, I shall not describe those which are already sufficiently well known, and in regard to which there is no manner of doubt or dispute. I shall restrict my descriptions to the doubtful or imperfectly known species, attempting at the same time to make their systematic arrangement more lucid and less complex.

It is a noticeable fact that in general works on the systematic relations of Molluscs, the diagnoses of the families and genera of Pteropods are always the same, and that from a comparatively ancient date, just as if they had been verbally copied by successive authors. And since they have not been modified with the progress of research, the result is that they are often incorrect. I have therefore taken particular care with the diagnoses of families and genera, and have based these on specimens which I have myself studied. The diagnoses I have framed as simply and methodically as possible.

My monographic study of the subgroup Thecosomata has been based upon the following collections :

1. The dry and preserved specimens in the British Museum.

2. The dry shells of Thecosomata in the Brussels Museum.

3. The Thecosomata collected on the “Triton” expedition.

4. The Thecosomata collected by Mr. John Rattray, F.R.S.E., during the cruise of the steamship Buccaneer” on the western coast of Tropical Africa (1885-86).

5. The Thecosomata collected by the Italian vessel “Vettor Pisani” during the scientific expedition round the world (1882-85).

6. The Pteropods captured by Surgeon David Bruce, M.B., near Malta (1886).

7. The Thecosomata collected at the Zoological Station at Naples during my stay there (from February to July 1887).

I must also gratefully acknowledge my indebtedness to Mr. Edgar A. Smith, of the Zoological Department of the British Museum, from whom I have received much assistance, to Professor Ch. Yelain, of Paris, and to Mr. W. H. Dali, of the U.S. National Museum.

After enumerating the species I shall discuss the geographical distribution of the group. The phylogenetic relations of the different genera can only be satisfactorily discussed after some treatment of the anatomy, and will therefore be discussed in the anatomical Report.

The Habits of the Thecosomatous Pteropods.

I have nothing to add here either in regard to the history of the group or the differ- ences between the two subdivisions. The subject has been sufficiently discussed in the Introduction to my Report on the Gymnosomatous Pteropods.1

1 Zool. Chall. Exp., part lviii. pp. 1-6.

REPORT ON THE PTEROPODA.

3

So too in regard to the habits of the Thecosomata. Like the Giymnosomata they are pelagic Molluscs, which descend to a certain depth to avoid bright light, and reascend when the light is feeble or absent, and when the sea is calm. They feed mainly on Protozoa (Radiolaria, Foraminifera, Infusoria) or on lower Algae, while the Gymnosomata prey upon decidedly higher animals. This difference of diet is the condition effecting the notable diversity in the structure of the alimentary system, and especially of the buccal and stomachic armature.

The Thecosomata of the Challenger Expedition.

The Thecosomatous Pteropods collected on the Challenger Expedition, which form the material bases of the present Report, comprise two distinct series :

1. The Thecosomata captured alive in the tow-nets, and preserved in alcohol or in microscopic preparations mounted in Canada balsam or in glycerine. These were entrusted to me towards the end of 1885 for use in my Report on the anatomy of the group.

2. The dry shells from deep-sea deposits, the importance of which will be discussed in the special report on the sea-bottom. This collection was selected from the deposits in the Challenger Office and also by Mr. Alfred E. Craven, who at one time proposed to write the Conchological Report on this group. It passed into my hands in the beginning of 1887, when a large number of the specimens had been already assorted.

I. The Thecosomata taken alive were gathered from seventy stations, and include twenty-eight species representing all the known genera. Among these species there is no new form, though a certain number have been hitherto insufficiently known or only once recorded.

The following table indicates the distribution of these species among the different genera.

Limacina,

Peraclis,

Clio, .

Cuvierina,

Cavolinia,

Cymbulia,

Gleba,

that is, among 7 genera, . . . .28 species.

II. The Thecosomata dredged from the deposits of the deep sea occur in all those known by the title Pteropod ooze,” and also in others. I have received the

1

10

1

8

1

1

4

THE VOYAGE OF H.M.S. CHALLENGE R.

shells from the sediments of twenty-one stations most rich in Thecosomata. The results of the study of these shells are detailed in this Report under the title of Deposit-shells.” In the different shell-containing sediments which I have examined, I have found twenty-four species of Thecosomata, of which a dozen occur in considerable abundance at many of the stations. One of these forms is quite new. The various forms are distri- buted as follows in the different genera

Genera.

Species previously known.

New Species.

Limacina, .....

6

Peraclis, .....

1

1

Clio, ......

8

Cuvierina, .....

1

Cavolinia, .....

7

...

Besides these twenty-four species there are five which do not occur in the Challenger collection of preserved Thecosomata. The total number of Pteropoda Thecosomata thus amounts to thirty-three, of which one is new, and a number either insufficiently known or not previously figured.

Limacina, ...... 8

Peraclis, ...... 2

Clio, . . . . . . .12

Cuvierina, ...... 1

Cavolinia, ...... 8

Cymbulia, ...... 1

Gleba, ...... 1

that is, in 7 genera, . . . . . .83 species.

DESCRIPTION OF GENERA AND SPECIES.

PiEROPODA, Cuvier. THECOSOMATA, cle Blainville.

Pterocephala, Wagner, 1885.1 Eupteropoda, Boas, 1886.2

THE GENERA AND FAMILIES OF THECOSOMATA.

In the Systematic Report on the Gymnosomatous Pteropods, I have noted a number of genera formerly included in the group Pteropoda, but which ought long ago to have been relegated elsewhere.

Among the Thecosomata too, a number of forms have been rather recently included which do not belong to the group of Pteropods. Such are, for instance, Cheletropis and Sinusigerci, which are really larvae of Streptoneural Gastropods, whose velum has been mistaken for a fin ;3 and as to Hcdopsyche ( Euribia and Psyche ), it is one of the Gymnosomata, as I have noted in my previous Report.

But even after abstracting the names of genera which ought without hesitation to be removed from the systematic nomenclature of Thecosomata, there remains a long list of titles, which have been invented for living forms realty belonging to the Thecosomata, but of which the majority cannot be retained. Such titles are proportionately more numerous than the generic names established for the Gymnosomata, and this because the generic diagnoses of the Thecosomata have been almost always based upon the shell. To this, which is nothing more than a simple ectodermic secretion, conchologists have attached too much systematic importance. There are indeed certain subgroups of Thecosomata, including a number of generic titles, greater than that of the genuine species.

1 Die Wirbellosen des weissen Meeres, Bd. i. p. 119.

2 Spolia atlantica, p. 179.

3 Gastropods of the family of Csecidae also have long been considered as Thecosomatous Pteropods, under the title Odontidium.

6

THE VOYAGE OF H.M.S. CHALLENGER.

Against such a tendency it is necessary to protest and to revert to a less rigid con- ception of what constitutes a genus, and though one does attach considerable systematic importance to the shell, this must not be exaggerated so as to lead to the erection of a separate genus for species which differ in some minute feature in the shell, but agree with one another in the rest of their characters. In addition to several differences of some importance in regard to the shells, it will be necessary to justify the establishment of a genus by at least one characteristic difference either in the soft structure of the animal, or in certain hard parts like the operculum or the buccal armature, which are generally of real importance in generic and specific diagnoses.

From this it follows that a large number of the generic titles discussed below must either .be abandoned or regarded as synonyms. Some of them again may be considered as designating generic subdivisions, though these are not in any way indispensable in so comparatively small a group as the Thecosomata.

I shall append, from the literature of the group, an alphabetical list of the various generic names given to living Thecosomata :

Agadina, Gould.

Archonta, Montfort. Balantium , Leach. Campylonaus, Gray. Cavolinia, Abildgaard. Cleodora, Peron and Lesueur. Clio, Linne.

Corolla, Dali.

Creseis, Rang.

Cuvieria, Rang, non Peron. Cuvier ina, Boas.

Cymbulia, Peron and Lesueur. Diacria, Gray.

Embolus, Jeffreys.

Euromus, H. and A. Adams. Gleba, Forsk&l.

Ileliconoides, d’Orbigny. Helicophora, Gray.

Heterofusus, Fleming.

Hyalsea, Lamarck.

Hyalocylis, Fol.

Limacina, Cuvier.

Orbignyia, A. Adams.

Peracle, Forbes.

Pleuropus, Eschscholtz.

Protomedea, 0. G. Costa.

Rheda, Humphreys.

Scsea, Philippi.

Spiratella, de Blainville.

Spirialis, Eydoux and Souleyet. Styliola, Lesueur.

Tiedemannia, delle Chiaje.

Tricla, Oken, non Retzius.

Triptera, Auctorum, non Quoy and Gaimard.

Of these thirty-four titles

I. Two ought to be provisionally set aside as doubtful, for reasons which I shall after- wards submit :

Agadina, Gould.

Triptera, Quoy. and Gaimard.

EEPOET ON THE PTEEOPODA.

7

II. Twenty-five are duplicates, and ought therefore to be retained simply as synonyms of Thecosomatous genera :

Archonta, Montfort, . Balantium, Leach, Campylonaus, Gray, . Cleoclora, Peron and Lesueur, . Corolla, Dali,

Creseis, Rang,

Cuvieria, Rang,

Diacria, Gray,

Embolus, Jeffreys,

Euromus, Adams,

LLeliconoides, d’Orbigny, Helicophora, Gray, Heterofusus, Fleming,

Hyalsea, Lamarck,

Hyalocylis, Fol,

Orbignyia, A. Adams, Pleuropus, Eschscholtz, Protomedea, 0. G. Costa, Rheda, Humphreys, .

Scsea, Philippi,

Spiratella, de Blainville, Spirialis, Eydoux and Souley et, Styliola, Lesueur, Tiedemannia, delle Chiaje, Tricla, Oken, .

= Carolina, Abildgaard. = Clio, Linne.

= Peraclis, Forbes.

= Clio, Linne.

= Gleba, Forskal.

= Clio, Linne.

= Curie rina, Boas.

= Cavolinia, Abildgaard. = Limacina, Cuvier.

= Peraclis, Forbes.

= Limacina, Cuvier.

Limacina, Cuvier.

Limacina, Cuvier.

= Cavolinia, Abildgaard. = Clio, Linne.

= Cavolinia, Abildgaard. = Cavolinia, Abildgaard. = Limacina, Cuvier.

= Cavolinia, Abildgaard. = Limacina, Cuvier.

Limacina, Cuvier.

Limacina, Cuvier.

= Clio, Linne.

= Gleba, Forskal.

Cavolinia, Abildgaard.

As to the genus Valvatina, Bornemann,1 Fischer2 is evidently in error in stating that it includes living Pteropods, for all the forms which he describes are fossils. It is like- wise probable that most of the latter are not even Pteropods.

The genera Euchilotheca, Fischer ; Flabellulum, Bellardi ; Gamopleura, Bellardi ; Poculina, Bellardi ; Tibiella, Meyer, and the genus Valvatina mentioned above are only known as Tertiary fossils ; and they are further very closely allied to various extant genera.

I completely abstract certain primary fossils usually referred to the Pteropoda. I

1 Die microscop ische Fauna des Septarienthones von Hermsdorf bei Berlin, Zeitsclir. d. deutsch. geol. Gesellsch., Bd. vii.

p. 18.

2 Manuel de Conchy liologie, p. 430.

8

THE VOYAGE OF H.M.S. CHALLENGER.

have a deep conviction that these organisms do not really belong to the group in question, and am firmly of opinion that Pteropods do not occur as fossils till the end of the Lower Tertiary. I shall afterwards revert more explicitly to this point in the anatomical part of the Report, in connection with the origin and phylogeny of the group.

Among the living Thecosomata really known there are, then, strictly speaking, only eight genera, including one new genus established in this Report.

These genera are :

Limacina, Cuvier. P ercicle, Forbes. Clio, Linne. Cuvierina, Boas.

Cavolinia, Abildgaard. Cymbulia, Peron and Lesueur. Cymbuliopsis, n. gen.

Gleba, Forsk&l.

The following table indicates the chief diagnostic characters :

Key to the Genera.

I. Calcareous shell quite outside the mantle.

1. Shell twisted into a spiral.

A. Shell with somewhat gentle whorls, a moderately wide opening, and a

columella not prolonged into a recurved rostrum, . . . .

B. Shell with rapidly ascending whorls, with a very wide opening and a

columella prolonged into a recurved rostrum, . . . .

2. Shell straight and bilaterally symmetrical.

A. Shell larger at the aperture than just behind.

a. Shell without constriction behind the aperture,

h. Shell with a constriction immediately behind the aperture,

B. Shell narrower at the aperture than just behind, . . . .

II. Cartilaginous shell covered by the pallial epithelium.

1. Voluminous shell with a marked cavity.

A. Thick shell, with the cavity not extending dorsally to the very end,

B. Shell with thin walls, cavity extending dorsally to the very end,

2. Flattened shell with almost no cavity, ......

Limacina.

Peraclis.

Clio.

Cuvierina.

Cavolinia.

Cymbulia.

Cymbuliopsis.

Gleba.

As to the relations of these eight genera with the other Pteropods, we have already noted in the Systematic Report on the Gymnosomata,1 that Fol doubts whether Cymbulia has not more affinity with the Gymnosomata than with the Thecosomata. Wagner also separates the genus Cymbulia from the Thecosomata, and in order to get over the difficulty without solving it, creates for these animals a third division among the Pteropods, viz., Alata.2

In reality the members of the genus Cymbulia do not differ from the typical Theco- somata which Souleyet included in his family Hyales” except in external appearance.

1 Zool. Chall. Exp., part lviii. p. 6.

2 Die Wirbellosen des weissen Meeres, Bd. i. p. 119.

EEPOET ON THE PTEEOPODA.

9

In their entire organisation (existence of a pallial cavity ; number of tentacles ; position of the penis, fins, cerebral ganglia, &c.) they agree with the Thecosomata, as we shall see in our anatomical Eeport. On the other hand, their special characters make it convenient to erect for them a special family, which appears to be a far preferable course to uniting them, as Woodward1 has done, with the Cavoliniidse, in which he has also included the Gymnosomatous Halopsyche.

As to the other Thecosomata, they form a more uniform group, within which one may pass from one form to another without remarking any very considerable modification. It is true, however, that in this group some forms differ from the majority in having the shell twisted into a spiral, as also in the position of the anus and of the pallial cavity. The existence of these last two differences in forms otherwise closely allied will be explained in the anatomical part of the Eeport. The differences just mentioned make it possible to separate the forms in question, and to erect them into the family Limacinkke, which, however, Souleyet unites with the typical Thecosomata.2

As to all the rest, they form a most natural family Cavoliniidse, from which there is no reason to separate the genus Cuvierinci, under the name of Tripteridse, as Gray 3 and the brothers Adams4 have done. The last mentioned genus in fact differs but very slightly from certain types of Cavoliniidse, such as the species of Clio of the section Creseis, from which indeed they are distinguishable only by the presence of a partition towards the middle of the shell, and by the constriction behind the aperture.

Among the Thecosomatous Pteropods, we thus recognise only three families :

1. Limacinidse, including the genera Limacina and Peraclis.

2. Cavoliniidse, ,, Clio, Cuvierma, and Cavolinia.

3. Cymbuliidse, ,, Cymbulia, Cymbuliopsis, and Gleba.

Family I. Limacinida

1847. Limacinidx , Gray, A List of the Genera of Eecent Mollusca, their synonyms and types, Proc. Zool. Soc. Lond., p. 203.

1859. Spirialidse, Chenu, Manuel de Conchyliologie, t. i. p. 113.

Characters. Shell external, twisted into a left-handed spiral, with a spiral oper- culum. Animal with a dorsal pallial cavity, and a ventral columellar muscle ; anus situated on the right side.

Description. The shell, which is always delicate as in other pelagic animals, is of small size, and is translucent with slight colouring. The spire and the operculum differ considerably in form in the various species.

1 A Manual of the Mollusca, p. 204, 1856. 2 Histoire naturelle des Mollusques Pteropodes, p. 32.

3 Catalogue of the Mollusca in the Collection of the British Museum, pt. ii., Pteropoda, p. 23.

4 The Genera of Recent Mollusca, vol. i. p. 54.

(zool. chall. EXP. PART LXV. 1887.)

Ttt 2

10

THE VOYAGE OF H.M.S. CHALLENGER.

The operculum is very delicate, glassy, and transparent. It is fixed by a portion of its surface to the posterior face of the ventral lobe of the foot.

The animal is twisted like the shell which it completely fills, and into which it may be completely retracted. The margin of the mantle bears, on the right-hand side, and somewhat ventrally, a long extensile appendage. The posterior lobe of the foot, which bears the operculum and is topographically ventral, is hollowed out on the middle of its free margin. The fins do not exhibit, towards their distal extremity, the area without muscular fibres which is usually to be observed in the genus Clio }

As regards the systematic relations of the genera and species, the family Limacinidse is still but imperfectly understood. This is in part doubtless due to the small size of the animals which form the family. They have hitherto been but rarely studied, and even in special works on Pteropods are often slurred over, as for instance in the memoirs of Quoy and Gaimard and of Rang. In the same way Troschel and Gegenbaur in their studies on the Pteropods of the Mediterranean have not discussed a single member of this family, and we may also note that Pfeffer, who has published an important description of the Thecosomata in the Hamburg Museum, has quite overlooked the Limacinidse.

The investigation of the numerous specimens of this family which were collected on the Challenger Expedition has enabled me to make an almost complete study of the entire family. The results of my investigation I therefore proceed to submit.

If one considers the living species alone, one finds in the literature of the subject that there are no less than thirty-six different specific names applied to forms referred to this family. In this number I do not include, be it understood, the manuscript species, or those which have been simply recorded without description or figure Limacina carinata, Jeffreys,2 Spirialis diversa, Monterosato,3 Spiricdis contorta, Monterosato.4 These I evidently could not take into account.

Since the work of Souleyet,5 Boas is the only naturalist who has attempted to make a synthetic study of this group.6

From the researches of these authors it may be concluded that there are now seven species adequately enough known by their shell, operculum, and anatomy to leave no doubt as their systematic position. These species are the following, and in citing them I shall retain the original generic titles, omitting for the present the discussion of their proper generic distribution.

1 Boas considers this space as corresponding to the hollow which separates the small tentacle-like lobe of the fin of some species of Limacina and Clio of the subgenus Creseis, from the margin of this fin (Spolia atlantica, p. 182, pi. v. figs. 70-79).

2 The French Deep-Sea Exploration in the Bay of Biscay, Rep. Brit. Assoc., 1880, p. 387.

3 Nuova rivista delle conchiglie Mediterranee, p. 50.

4 Ibid., p. 50.

5 Histoire naturelle des Mollusques Pteropodes.

6 Spolia atlantica, pp. 38-50.

REPORT ON THE PTEROPODA.

11

1. Atlanta injlata, d’Orbigny.

2. Atlanta lesueurii, d’Orbigny.

3. Clio helicina, Pliipps.

4. Spirialis australis, Eydoux and Souleyet.

5. Limacina balea, Moller.

6. Atlanta trochiformis, d’Orbigny.

7. Atlanta bulimoides, d’Orbigny.

The considerable number (twenty-nine) of other forms described (often very imperfectly, and without examination of the animals) includes the following forms. I should rather say did include the following when I undertook this Report, for as the result of the investigation about to be recounted, certain changes in the grouping become necessary. Thus one species in Group III. must be referred to Group I., while two species of Group II. must be placed at the end of the seven species chronicled above.

I. One, which I cannot regard as a Pteropod : Limacina turritelloides, Boas.

II. Four, which appear to me to belong quite clearly to the Thecosomatous Limacinidse :

Embolus triacanthus, Fischer. Limacina helicoides, Jeffreys.

Limacina antarctica, Woodward. Atlanta reticulata, d’Orbigny.

III. Four, which seem to me much less certain, but in regard to which the reports of those who have studied them are not sufficient to admit of a positive conclusion as in the case of the two preceding groups. Until further information is forthcoming they must be regarded as doubtful :

Limacina (?) cucullata, Gould. Agadina stimpsoni, A. Adams.

Agadina gouldi, A. Adams. Atlanta rotunda, d’Orbigny.

IV. Finally, all the other specific titles are synonyms either of some of the seven well-known species, or of the four included in the second group :

Argonauta artica, Fabricius, .

Limacina helicialis, Lamarck, . Spiratella limacina, de Blainville, Limacina pacifica, Dali,

Peracle jlemingii, Forbes,

Limacina balea, Moller,

Scaea stenogyra, Philippi,

Spirialis goiddii, Stimpson,

Spirialis Jeffrey sii, Forbes and Hanley, . Spirialis macandrei, Forbes and Hanley, Heterofusus alexandri, Verrill,

Limacina naticoides, Rang,

j> = Clio helicina, Phipps.

= Heterofusus retroversus, Fleming.

= Atlanta trochiformis, d’Orbigny.

12

THE VOYAGE OF H.M.S. CHALLENGER.

| = Atlanta lesueurii, d’Orbigny.

\ = Atlanta injlata, d’Orbigny.

J

= Atlanta reticulata, d’Orbigny.

To these known species I can also add a new form included in the Challenger collection, which may without hesitation be referred to Group II. of undoubted Limacinidse. Another form, which cannot be identified with any of those hitherto known, seemed at first to be referable to Group III. above, but subsequent examination has shown that it must rather be placed in Group I. aloug with another species of the same nature.

How are these different species to be distributed throughout the family ? Or, in other words, how many distinct genera can be distinguished.

The question is indeed a most difficult one, and there are almost as many opinions on the subject as there are investigators of the group. Very few of the expressed opinions, however, claim much serious attention, for there has hardly been any previous attempt to make a systematic synthesis of the family Limacinidse.

If we turn to the table of genera (p. 8) we see that twelve generic titles have been invented for living Thecosomata with spiral twisting, that is to say, just the same number of genera as there are certainly admissible species. I append the titles in chronological order :

Atlanta rangii, d’Orbigny (?), .

Spirialis ventricosa, Eydoux and Souleyet, Spirialis rostralis, Eydoux and Souleyet, Protomedea elata, 0. G. Costa,

Limacina scaphoidea, Gould, .

P eracle physoides, Forbes,

Spirialis clathrata, Eydoux and Souleyet, Spirialis recurvirostra, A. Costa,

1. Limacina, Cuvier, 1817.

2. Heterofusus, Fleming, 1823.

3. Spiratella, de Blainville, 1824,

4. Heliconoides, d’Orbigny, 1836.

5. Spirialis, Eydoux and Souleyet, 1840.

6. Helicophora, Gray, 1842.

7. P eracle, Forbes, 1844.

8. Scsea, Philippi, 1844.

9. Campylonaus, Gray, 1847.

10. Euromus, A. and H. Adams, 1858.

11. Protomedea, 0. G. Costa, 1861.

12. Embolus, Jeffreys, 1869.

What increases the confusion resulting from this superfluity of generic nomenclature in a group with so few forms, is the fact that several of these names have been used in different ways by different authors. Hence a complex and contradictory set of synonyms.

REPORT ON THE PTEROPODA.

13

Gray (1850),1 Gould (1852), 2 and Boas (1886) 3 have tried to simplify the matter by uniting all the known species in a single genus with the oldest title, Limacina, Cuvier. But it must be noted that Gould knew but few species of Limacinidse, and that for one form which he regarded as new he even thought that it might be well to create a new genus. Jeffreys 4 also unites in a single genus, Limacina, all the species which he discusses except Atlanta inflata, d’Orbigny, for which he establishes a genus Embolus, although a certain species which he calls Limacina. i differs more from the typical Limacina than does Atlanta inflata. And besides, as we shall afterwards see, that solution of the difficulty which seeks to unite in a single genus all the living Limacinidse is not in conformity with the differences of organisation exhibited by the various types.

There is only one way of restoring order to the confused nomenclature, and that is to find for each generic title the connotation given to it by its inventor, and the type to which it was originally applied. In this way alone can one recognise with any certainty what are the synonymous titles, and eliminate the more recent tautologies.

Let us then see what titles ought to be expelled from the nomenclature.

I. It is necessary first of all to abstract the genus Agadina, Gould, which, as we shall immediately see, has been too inadequately and imperfectly diagnosed to admit of any accurate conception being framed in regard to the organisms to which it ought to be applied.

II. The genus Spiratella was founded in 1824 by de Blainville for Clio helicina, Phipps. But for the same species the genus Limacina was erected by Cuvier in 1817. The name Spiratella need not therefore be retained.

III. The genera llcliconoides, d’Orbigny (1836), Spirialis, Eydoux and Souleyet (1840), and Helicophora, Gray (1842), are all based upon the same series of small forms, but without reference to any particular type. This series includes among its species three forms of shell, and to this it is due that the above titles have been used with different connotations by different authors (the brothers Adams, Bronn, Carus, Fol, Sars, &c.).

These forms of shell are (1) a more or less elevated spiral with a simple lip ; (2) a depressed spiral with a rostrated lip ; and (3) with a very large aperture and a columella prolonged into the rostrum ; and they have all received different names. The adoption of these new names evidently involves the abandonment of the titles noted above in the original sense of their authors. The new names corresponding to the three forms of shell are as follows :

1 Catalogue of the Mollusca in the Collection of the British Museum, pt. ii., Pteropoda.

2 The Mollusca and Shells of the U.S. Exploring Expedition.

3 Spolia atlantica.

4 New and peculiar Mollusca, &c., procured in the Valorous Expedition, Ann. and Mag. Nat. Hist., ser. 4, vol. xix. p. 337.

14

THE VOYAGE OF H.M.S. CHALLENGES.

1. Heterofusus, Fleming (1823), and Scaea, Philippi (1844) ; the former based on Heterofusus retroversus, Fleming, the latter on Scsea stenogyrci, Philippi. But as these two species are identical, the two generic titles are absolutely synonymous, and the more recent ought to disappear.

2. Protomedea, 0. G. Costa (1861), and Embolus, Jeffreys (1859) ; the former based on Protomedea elata, 0. G. Costa, and the latter on Atlanta injlata, d’Orbigny. But as the two species are synonymous, the two generic titles are equally so ; and since the name Protomedea was applied in 1834, by de Blainville, to a Coelenterate, it ought to disappear.

3. Peracle, Forbes (1844), Campylonaus, Gray (1847), and Euromus, A. and H. Adams (1858) : the two last based on Atlanta reticulata, d’Orbigny ( = Spirialis clathrata, Eydoux and Souleyet). and the first on Peracle physoides, Forbes. But as these two specific types are now recognised to be identical, the three generic titles are obviously so too, and the two more recent ought to be disused.

Having reached this stage of our critical review, we see that the maximum number of generic titles which can be adopted for the Limacinidse does not exceed those four Limacina, Heterofusus, Embolus, and Peracle since we may abstract Heliconoides ( = Spirialis Helicophor a), this genus being succeeded by the three generic titles referring to the three forms of shell which it includes.

But are Heterofusus and Embolus really distinct, with this simple difference, that in the second the spire is depressed and the lip rostrate ? This can hardly be, for in almost all the genera of Gastropods there are species with short and others with elongated spirals, and the same is true of the rostrate lip. Thus in a group adjacent to the Limacinidse, the important genus Clio ( = Cleodora) exhibits nearly related species, some with a rostrum on the dorsal surface and others without. Nevertheless these forms are much too closely allied to be generically separated, and ought not the same to apply to Heterofusus and Embolus ? Both exhibit in fact an umbilicate shell, with whorls increasing somewhat gently, and a semilunar operculum, with a right-handed spiral of few turns ; nor do the animals exhibit any difference in their structure.

But besides having these characters in common, they share them with Limacina, from which they do not differ in any character sufficient to establish a generic distinction, although, as I have already noted, the reverse has been maintained by Gray, Gould, Boas, and to a certain extent by Jeffreys. It must be remarked on the other hand that Souleyet, who created the genus Spirialis (including Heterofusus and Embolus), recognised that it ought to be united with Limacina if there were an operculum in the latter.1 But it is now sufficiently demonstrated that in Limacina an operculum does exist.

It is true that Sars maintains the generic distinction of Limacina and Spirialis (in

1 Voyage de la Bonite, Zoologie, t. ii. p. 211.

REPORT OX THE PTEROPODA.

15

the restricted sense of Heterofusus), principally on the ground of the transverse strise (at right angles to the axis), which are found in Lirnacina helicina. But this character cannot be regarded as of the value of a generic distinction. If we turn for instance to a group but slightly removed from the Limacinidae, the species of Clio of the subgenus Creseis, we see that Clio chierchiae, Boas, also possesses these transverse strise which are wholly absent in the other three species of the same subgenus. Yet one would not on that account dream of establishing a generic distinction on that simple fact, and a fortiori one cannot separate Lirnacina (s. str.) from Spirialis.”

As to the genus Peraclis, Forbes, it is so distinct that it must be retained, although d’Orbigny has referred its typical species to Heliconoides, Souleyet and A. Costa to Spirialis, and Gray, Jeffreys, and Boas to Lirnacina.

Peraclis differs indeed from the genus Lirnacina (as this has been defined above) in having a shell which is not umbilicate, has a few whorls ascending very rapidly, a larger aperture, a columella prolonged into a rostrum twisted into a spiral, and, further, in possessing a subcircular operculum, with a multispiral, left-handed coil. To this operculum neither d’Orbigny, Souleyet, nor Boas have attached the degree of import- ance demanded by its peculiar structure. But even if we do not take account of these differences, the structure of certain portions of the animal of Peraclis separates it markedly from all other Limacinidae, as we shall afterward see, and necessitates the formation of a distinct group, opposed to all the rest of the family.

From the foregoing it results that there are among the living Limacinidae only two different genera, Lirnacina and Peraclis, which may be readily distinguished by turning to the synoptic table of genera (p. 8).

Lirnacina / Cuvier.

1817. Lirnacina, Cuvier, Le Regne animal, t. ii. p. 380.

1823. Heterofusus, Fleming, On a reversed species of Eusus, Mem. Wern. Soc., p. 498.

1824. Spiratella, de Blainville, Mollusques, Diet. d. Sci. Nat., t. xxxii. p. 284, iv. p.

1836. Heliconoides, d’Orbigny (pars), Voyage dans l’Amerique meridionale, t. v. p. 174.

1840. Spirialis, Eydoux et Souleyet (pars), Description sommaire de plusieurs Pteropodes nouveaux ou imparfaitement connus, Rev. Zool., t. iii. p. 235.

1842. Helicophora, Gray, Synopsis of the contents of the British Museum, p. 59.

1844. Scxa, Philippi, Fauna Molluscorum utriusque Siciliie, p. 164.

1861. Protomedea, G. O. Costa {pars), Microdoride Mediterranea, p. 73.

1869. Embolus, Jeflreys, British Conchology, vol. v. p. 114.

Shell umbilicate, with turns gradually increasing ; with a fairly large aperture ; and with a columella not prolonged into a rostrum ; surface smooth or striated. The height of the spire, the form of the surface and that of the aperture, and the size of the

1 Diminutive of Limax.

16

THE VOYAGE OF H.M.S. CHALLENGER.

umbilicus vary according to the species. Operculum semilunar, with a right-handed spiral of a few whorls.

Animal with an indistinctly defined head, which is only marked externally (1) by the lips on the border of the mouth and (2) by the tentacles.

1. Lips : two dorso- ventral folds on the cephalic surface of the fins, united dorsally, diverging ventrally, where they are continued by a fold of the cephalic surface of the fins, and extend laterally to the edge of the fins. They thus enclose a ciliated area which plays an important part in alimentation.1 The mouth, split dorso- ventrally, is situated between these lips, in the angle formed by their union.

2. Tentacles, asymmetrical, the left always less developed and further back than the right. The latter is very long and retractile into a sheath. The tentacles thus exhibit absolutely the same form as those of the Cavoliniidse. Souleyet2 noted that in Limacina helicina the right tentacle seemed to be situated in a sheath, and3 that in his Spirialis the minuteness of the organs did not permit him