BULLION. 409 



lias the precedence. Our shell varies in thinness^ in 

 comparative length and breadth, and in the turgidity of 

 the body-whorl. 0. carnea is not uncommon in the 

 Mediterranean; the young is probably Risso^s Siinnia 

 nicceensis. 



Order IV. PLEUROBRANCHIATA, Gray. 

 (See Vol. III. p. 200.) 



In the same year that Dr. Gray proposed the name 

 which I have adopted for this order, Professor Loven pub- 

 lished another name, viz. Pomatobranchia. I now place 

 it immediately after the Siphonobranchiata, and post- 

 pone the Pulmonobranchiata (as being more perfect 

 Gastropods) not only to the present order, but also to 

 the Nudibranchiata and Pellibranchiata. I accidentally 

 omitted in page 265 '' Order III. SIPHONOBRAN- 

 CHIATA/^ The families Cerithiopsidce to Cyprceidcp 

 inclusive belong to the last-named order ; and the num- 

 bers prefixed to them (viz. XXVI. to XXXI.) ought 

 therefore to be I. to VI. 



Family I. BUL'LID^, (Bidladw) Clark. 



Body gelatinous, generally divided into separate parts or 

 lobes, and not always containable within the shell : ?iea(/ 

 snout-shaped : tentacles either united and forming a hood or 

 head-veil, or consisting of two distinct and broad lappets : 

 eyes, when present, sessile or subcutaneous, at the base of the 

 tentacles or at the sides of the head : foot usually large, some- 

 times expanded on each side, like fins {epipodia) whicli serve 

 for swimming, as well as behind into a single lobe (meta- 

 podium), so as to cover the crown or apex of the shell : r/iUs 

 forming a single triangular plume, which is placed across the 

 back on the right side, and protected by the shell : gizzard 

 peculiar to most (if not all) genera, and composed ( F several 



VOL. IV. T 



