272 BULLID A. 
very common Linnean 4d. depilans, which may be seen in 
certain seasons, at Exmouth, in thousands, feeding on the 
Algee of the littoral districts. 
APLYSIA, Linneus. 
A. DEPILANS, Pennant et Auct. 
A. hybrida, Brit. Moll. ui. p. 554, pl. 114. F. f. 4; (animal) pl. Y.Y. f. 1. 
BULLID A. 
The Bullide 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, Bullea, 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; im 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 Bullea 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 
