AC ERA. 429 



U. pellucidus of Brown is the adult, his U. minutus 

 the half-grown shell, and his U. candidus the young ; 

 Gould described this species as Bulla debilis, and Moller 

 as B. subangulata. It is not the B. hyalina of Gmelin. 



Genus III. A'CEBA* (Akera) MiiUer. PL VIII. f. 3. 



BODY gelatinous, not containable within the shell : mantle 

 forming at the rear a cylindrical or thread-shaped process, 

 which occupies a slit in the front of the spire when the animal 

 is at rest : head snout-like and extensile : tentacles none : eyes 

 placed on each side of the head, near the front : foot very large 

 and flexible, expanding into broad wing-like lobes (one on 

 each side), which fold back over the shell and front of the 

 body, a great part of which is covered by them : gizzard horny. 



SHELL tumid, very thin and elastic : spire exposed, and trun- 

 cated : whorls angulated or keeled at the top ; the first is 

 nipple-shaped, and the last is partly separated from the pre- 

 ceding one : suture deeply excavated : mouth occupying nearly 

 the whole length of the shell, open in front and contracted 

 behind : pillar sharp-edged : no operculum. 



Perhaps this and Bulla subsist on soft organisms; 

 their gizzards seem adapted to such food, not being, 

 like the calcareous millstones with which Scaphander 

 and Philine are provided, strong enough to crush hard 

 shells. The odontophore or tongue of Acera is broad, 

 and has numerous spines in each row ; that of Utriculus 

 is narrow, and has only two spines in a row. The shell 

 consists of two layers the inner one membranous, and 

 the outer testaceous. 



It is not the "Acere" or Bulla carnosa of Cuvier 

 (Acera, Lamarck) , which belongs to the Aplysia family 

 and is shelless. Leach called the present genus 

 Eucampe. 



* Without horns (or tentacles). 



