272 BULLION. 



very common Linnsean A. depilans, which may be seen in 

 certain seasons, at Exmouth, in thousands, feeding on the 

 Algse of the littoral districts. 



APLYSIA, Linnaeus. 



A. DEPILANS, Pennant et Auct. 

 A. hybrida, Brit. Moll. iii. p. 554, pi. 114. F. f. 4; (animal) pl.Y.Y. f. 1. 



BULLID^E. 



The Bullida which inhabit the South Devon coast at Ex- 

 mouth are deposited in two groups, which undoubtedly as to 

 essentials are of the same tribe, and have long been adopted : 

 the one, Bulla, of which the B. hydatis and B. lignaria are 

 the types, receives the species with external hard parts ; the 

 other, Bullcea, is represented by B. aperta, and is the re- 

 ceptacle of those with concealed shells. From these roots 

 some new genera have sprung, to meet the supposed require- 

 ments of modern discoveries, most of which are very minute ; 

 some are without eyes, all are without distinct tentacula, or 

 with the mere rudiments of them, and have the pedal lobe 

 more or less reflected laterally on itself, and partially on the 

 anterior end of the shell; in others the lax margins of the 

 deep sinus, at the under part of the foot, which separate it 

 from the linear posterior portion, occasion it to appear nearly 

 as simple as in the usual run of the Gasteropoda ; this latter 

 circumstance has led to some mistakes, as will appear in 

 the descriptions of the minute species. 



All the species I have met with have the invariable distin- 

 guishing character of the tribe, the gizzard consisting of three 

 testaceous, coriaceous or cartilaginous plates. I believe that 

 every true Bulla and Bullaea have one or the other of these 

 appendages ; indeed it may be considered, that if an animal, 

 however much it appears by the shell to belong to this family, 

 has not the shibboleth of the gizzard, it is an alien to it. 



The new genera of this tribe have been established by 



