MOLLUSCA.—CLASS IV. PTEROPODA. 277 
Hyalea cuspidata, Lamarck. D’Orbigny. 
Cleodora Lessoni, Rang. 
LIMACINA, Cuvier. 
Testa hyalina, spiralis, oblique discoidea, lateribus umbilicatis ; dorsim 
carinata, carina membranacea, lamellari; apertura ampla, integra, 
utrinque paululim inflata. 
The Pteropoda, though agreeing very closely with each other in their 
general organization and habits, appear to be provided with very anoma- 
lous kinds of shells ; they vary, indeed, so materially in their manner of 
growth and complete structure, that we should have supposed them to 
belong to animals differing considerably from each other in their ana- 
tomical peculiarities. The little glass shell, of which we are now to 
treat, described by Cuvier under the generic title of Limacina, is of com- 
plete nautiloid structure, and, like the shell of the Argonaut, is entirely 
destitute of any internal partition. De Blainville, struck with the great 
similarity of formation that exists between these shells, has gone so far 
as to pronounce the shell of the Argonaut to belong to some huge Ptero- 
pod; for in his ‘ Manuel de Malacologie,’ p. 494, the Argonaut, the 
Limacina under the title of Spiratella*, and a variety of it under that 
of Atlanta, are associated together in a particular family by themselves. 
The little that is at present known of the Limacinz is not sufficient even 
to modify the arrangement of Cuvier, but our recent discoveries respect- 
ing the Argonaut have fully determined its cephalopodous and distinct 
nature. 
The shell of Limacina may be described as being hyaline, spiral, ob- 
liquely discoid, umbilicated on each side, and carinated round the back 
with a membranaceous lamellar keel ; the aperture is large and entire, 
and it is slightly inflated on each side. 
* The title of Spiratella was introduced by De Blainville on account of the resemblance 
of the word Limacina to Limacinea, a name already used in reference to a family of land 
mollusks. 
VOL. II. 20 
