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. 
f Central series of lingual pavement absent. 
Cheek-pouches deep and tentacular 
(Having a lingual pavement, dental 
Gymnosomata. cheek-pouches, and å membra- suckers large and well-developed ....  PNEUMODERMON. 
Animal naked, head | nous envelope .............. | Central series of lingual pavement present. 
distinct. No gas- Buccal pouches shallow, and tentacular 
tric teeth appa- Having a triserial lingual strap, | suckers minute or rudimentary ...... Cr10. 
AP nee numerous and minute lateral 
labial plates cutting longitudi- 
t TT eere eere IRI . Evnvsn. 
( Shell cartilaginous (symmetrical) ; 
Thecosomata. (lod EN NNN CyMBULIA. 
Animal protected by Commissures of the 
a shell, with the ( With lateral slits through aperture closed.. Hyauza. 
head indistinct. which processes of the 4 
DET mantle protrude ...... | Lateral slits com- = 
Having a triserial municating with 
i ribbon, 4 Shell L the aperture. ... DIACRIA. 
large and definite Få eng Parietes angular or com- 
lateral labial erg pressed antero-posteriorly ........ CLIODORA. 
plates ^ cutting Lateral Pil af Subeylindrical, 
transversely, and hoe eon Pon apex decollated. — Cuvizru. 
two or more gas- | Shell calcareous ; entire and smooth or 
tric teeth ...... gastric teeth < crimped. trans. | Acuminate, apex 
| more than 2.. D vermely .... [. entre v i s ÜRESEIS. 
Inoperculate...... LImacIna. 
Shell sinistrally spiral........:... 
Operculate ...... SPIRIALIS. 
It will 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 Oliide, Eurybiide, and Hyaleide, the principal 
amendment of the commonly received arrangement being the separation of Hurybia frome — 
the Hyaleide, with which it has been improperly associated; and the union of the Zima- — 
cinide with the same family, from which they have been unnecessarily dismembered. 
The oe 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. 
* Th; : à * >. S. 
ng table is advanced with à little more confidence as, it has nets by the revising hand of Mr. W. 
