18 BULLIDiE. 



Genus akera, O. F. Miiller. 



Head-disk elongated, entire behind ; eyes none. Mantle 

 with a fimbriated edge projecting through the slit in the 

 spire. Foot with the lateral lobes greatly dilated, folded, 

 in repose, over the sides of the shell. 



Shell convolute, ovate or sub-cylindrical, ventricose, thin, 

 elastic ; spire truncated, the whorls distinct, channelled, 

 the last whorl disjoined from the others at the suture ; 

 aperture elongate, pyriform, rounded and entire in front; 

 inner-lip excavated; outer lip posteriorly free, angulated. 



Si/n. Acera, Latr., not Albers. Eucampe, Leach. Vi- 

 trella, Swains. 



Ex. A. soluta, Chemnitz, pi. 57, fig. 3. Shell, A. so- 

 luta, fig. 3, a. 



In this genus the head-disk is greatly elongated, wide 

 and bifid anteriorly, and narrowed posteriorly ; the hind 

 edge of the mantle is fimbriated and projects through the 

 fissured suture of the shell, the foot is expanded, narrow 

 and rounded anteriorly, and broad and truncated pos- 

 teriorly ; by means of the extended lateral foot-lobes the 

 animal, like Aglaia, swims with considerable facility, but 

 when crawling, the foot, as in that genus, is folded over 

 the back. 



S})ecies of Akera. 



bicincta, Quoy and Oaxm. subangulata, Moll. 



bullata, Mull. tenuis, A. Adams. 



soluta, Chem. tumida, A Adams. 



