CLASS III. GASTEROPODA. ORDER V. NUCLEOBRANCHIATA. 55 
habits, that authors have been for a long time divided upon the pro- 
priety of separating them. For our own part, we see no reason to depart 
from the arrangement of Cuvier and Lamarck, and therefore retain the 
genus Dolabella, describing the shell to be internal and calcareous, though 
sometimes partially horny ; generally more or less covered with a horny 
integument, and in shape somewhat resembling a hatchet ; the posterior 
side is narrow, thicker, somewhat spiral, and a little reflected over at the 
edge ; the anterior side is smooth, wider, and entire at the margin. 
Example. 
Pl. CLVII. Fig. 1 and 2. 
Dotapetta Rumpus, Cuvier, Ann, du Mus., vol. v. p. 437. pl. 29. f.r. 
De Blainville, Manuel de Malacologie, p. 473. pl. 43. f. 5. 
Limax marina, Rumphius. 
Doris verrucosa, Gmelin. 
Aplysia Rumphi (2), Deshayes, &c. 
Order V. GASTEROPODA NUCLEOBRANCHIATA. 
Branchiz plumatz, in nucleo dorsali coalite ; nucleo testa vitrea pellu- 
cida obtecto. 
We have now to describe a class of mollusks exhibiting a more distinct 
peculiarity of organization than any that have been yet noticed. They 
have received the above title on account of their branchiz, which are 
feathered, being enclosed in a lump or nucleus protruding from the back, 
and this nucleus is covered with a transparent glassy shell, in a manner 
distantly analogous to the way in which the branchial cavity is protected 
in the Aplysie. This is indeed the only reason that can be assigned for 
placing them in the immediate vicinity of that genus ; for although the 
general type of their organization agrees with that of the Gasteropoda, it 
