38 PLEUROBRANCHINJ!. 



Shell calcareous and external ; membranous and inter- 

 nal ; or, rarely, altogether wanting. 



The animals of this family have no upper jaw; the lin- 

 gual membrane is armed with numerous short teeth, ar- 

 ranged in a quincunx ; there are four stomachs, the second 

 of which is fleshy and sometimes furnished with bony 

 pieces, and the third is provided internally with prominent 

 longitudinal lamella? ; the intestinal canal is short. The 

 species of this group are tolerably numerous, occasionally 

 of large size and adorned with varied colours ; they arc 

 mostly inhabitants of the high seas. 



Sub-fam. PLEUROBRANCHIN^. 



Mantle covering and concealing the shell. 

 Shell, internal and rudimentary, membranous, or 

 altogether wanting. 



Genus PLEUROBRANCHUS, Cuvier. 



Tentacles dorsal, ear-like; labial appendages trans- 

 verse, folded, and truncate. Mantle smaller than the 

 foot, only partly covering the head, simple behind. Foot 

 very large, extending beyond the mantle. 



Shell internal, convex, thin, oval, membranaceous. 



Syn. Berthella, Blainv. Discoides, Renter. Cle- 

 anthus, Leach. 



Ex. P. citrinus, Riippell, pi. 60, fig. 4, 4, a. Shell, 

 P. plumula, Montagu, fig. 4, b. 



The Pleurobranchi live in families, under large stones, 

 in shallow water ; they feed on the sea-weed that grows 



