CONCHOLOGY. 95 
FAMILY IV. 
Buutacea. ‘Three genera. 
1. Genus Acera. 
Animal. Body ovate, convex, transversely divided above into 
two parts; the foot with dilations in the form of wings below ; 
head indistinct; branchie situated on the back, greatly behind, 
and covered by a mantle destitute ofa shell. Inhabits the Medi- 
terranean. One species. 
Acera carnosa. 
2. Genus Bullza. Pl. X. 
Animal. Body ovate, somewhat convex above, and divided 
into two parts transversely; lateral lobes of the foot very thick ; 
head indistinct, and without tentacula; branchie placed on the 
back. 
“Shell. Concealed in the mantle, very thin, rolled and spiral 
on one side; without a columella and spire ; aperture very large 
and wide, dilated at the upper part. Inhabits the British seas. 
Two species. 
Bullea aperta. Bullea striata. 
3. Genus Bulla. Pl. X. 
_ Animal. Body oblong ovate, slight convexity ; divided into 
two portions transverse above, mantle slightly folded posteriorly ; 
visible tentacula ; branchie dorsal and covered, opening only on 
the right side. 
Shell. Univalve, ovate globular, convolute, no columeila, spire 
not projecting but visible, aperture the whole length of the shell, 
external margin sharp and smooth. Inhabits the British and 
American seas. Nineteen species. 
Bulla physis. Bulla fragilis. 
B. naucum. B. aplustre. 
B. hydatis. B. ampulla. 
B. rugosa. B. lignaria. 
