248 



MR. J. D. MACDONALD ON THE ANATOMY OF EURYBIA GAUDICHAUDI. 



In the following synopsis of the principal genera of Pteropoda, Eurybia occupies a 

 position suggested by general anatomical principles, and which I believe to be the 

 natural one*. 



PTEROPODA. 



Gymnosomata . 

 Animal naked, head 

 distinct. No gas-^ 

 trie teeth appa-* Havinj 

 rent 



fCentral series of lingual pavement absent. 

 "Having a lingual pavement, dental | Cheek-pouches deep and tentacular 

 cheek-pouches, and a membra- J suckers large and well-developed .... 



nous envelope 1 Central series of lingual pavement present. 



Buccal pouches shallow, and tentacular 



Pneumodermon. 



a triserial lingual strap, (^ 

 numerous and minute lateral 

 labial plates cutting longitudi- 

 nally, and a cartilaginous mantle. . . 



suckers minute or rudimentary Clio. 



Thecosomota. 

 Animal protected by 

 a shell, with the 

 head indistinct. 



f Shell cartilaginous (symmetrical) ; 

 gastric teeth 2 



Having a triserial 

 lingual ribbon,-^ 

 large and definite 

 lateral labial 

 plates cutting 

 transversely, and 

 two or more gas- 

 tric teeth 



Shell calcareous ; 

 gastric teeth 

 more than 2. . 



- Shell 

 symme- 

 trical 



Commissures of the 

 'With lateral slits through aperture closed. . 

 which processes of the 



mantle protrude ; Lateral slits com- 



j municating with 

 1^ the aperture. . . . 

 "Parietes angular or com- 

 pressed antero-postcriorly 



Lateral n , . fSubcvlindrical, 



, , J Parietes round ■' , u . i 



borders< , ., ape.\ decollated. 



I and smooth or I "^ 



eutn-e . , . -, 



crnnped trans- . . , 



', Acuminate, aitex 



versely ! .• ■ 



•" L entire ....... 



Shell dinistrally spiral. 



L 



flnoperculate. 



< 

 LOperculate . 



Eurybia. 



Cymbulia. 



HYAL.EA. 

 DiACRIA. 



Cliodora. 

 cuvieria. 



Creseis. 



LiMACINA. 

 SPIRIALIS. 



It wUl be seen by the Table, that Eurybia differs still further from the true Thecoso- 

 mata in the peculiar structure of its labial dental organs (whose cutting edges run longi- 

 tudinally, not transversely), and in the total absence of gastric teeth. 



The members of the last division, having calcareous shells, are too closely related by 

 their internal anatomy to admit of their separation into two distinct families ; and I am 

 much inclined to believe, though not certain, that Cymbulia ought to be received amongst 

 them. The families thus indicated are the Cliidce, Eiirybiidce, and Hyalceiilce, the principal 

 amendment of the commonly received arrangement being the separation of Eurybia from 

 the HyalcBidce, with which it has been improperly associated ; and the union of the lAma- 

 cinidcB with the same family, from which they have been unnecessarily dismembered. 

 The species of Spirialis occurring in these seas may be truly described as the soft parts 

 of Creseis occupying a spiral operculate shell aping that of the Gasteropod. 



* This table is advanced with a little more confidence as, it has benefited by the revising hand of Mr. W. S. 

 MacLeay. 



