CONCHOLOGY. 8J> 



Ancylus lacustris. Ancylus fluviatilis. 



A. spinarosae. 



FAMILY IV. 



BuLLACEA. Three genera. 



1. Genus Accra. 



Animal. Body ovate, convex, transversely divided above into 

 two parts ; the foot with dilations in the form of wings below ; 

 head indistinct ; branchiae situated on the back, greatly behind, 

 and covered by a mantle destitute of a shell. Inhabits the Medi- 

 terranean. One species. 



Accra carnosa. 



2. Genus Bullsea. PI. 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 ; branchiae 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 uper part. Inhabits the British seas. 

 Two species. 



Bullsea aperta. BuUaea striata. 



3. Genus Bulla. PI. X. 



Animal. Body oblong ovate, slight convexity ; divided into 

 two portions transverse above, mantle slightly fold posteriorly ; 

 visible tentacula ; branchiae dorsal, and covered, opening only 

 on the right side. 



Shell. Univalve, ovate globular, convolute, no columella, spire 

 not projecting but visible, aperture the whole length of the shell, 

 external margin sharp and smooth. Inhabits the British seas* 

 Fourteen species. 



Bulla physis. Bulla fragilis. 



B. naucum. B. aplustre. 



