CONCHOLOGY. 83 



Shell. Sessile, univalve, rather globular, ventricose, convex 

 above ; apex perforated ; aperture small, elliptical, operculum 

 quadrivalve. Inhabits the Indian seas. One species. 

 Pyrgoma cancellata. 



7. Genus Anatifera. PI. V. 



Animal. Body covered with a shell, supported by a long 

 tubular tendinous peduncle ; with long, numerous, and unequal 

 tentacular arms, which are articulated and ciliated, and emanating 

 from the summit on one side. 



Shell. Compressed on the sides, with five flat valves, the valves 

 contiguous and unequal; the lower lateral ones the largest : the 

 whole of them united and kept together by means of their mem- 

 branes. Inhabits the British seas. Six species. 



Anatifera Isvis. Anatifera dentata. 



A. villosa. A. striata. 



A. vitrea. A. aculeata. 



8. Genus PolUcipes. PI. V. 



Animal. Body covered by a shell, and supported on a tabular, 

 tendinous, scaly peduncle ; with many tentacular arms. 



Sliell. Consisting of thirteen or more valves, the smallest at 

 the sides, which are very flat and compressed, the peduncle short, 

 wrinkled, rigid, and often covered with scales like shagreen. 

 Inhabits the European and American seas. Six species. 

 PolUcipes cornucopia. PolUcipes mitella. 



P. scalpellum. P. peronii. 



P. homii. 



P. Mortoni.* 



9. Genus Cineras. PI. V. 



Aiwnal. Body pedunculated, and encased in a membranous 

 tunic, which is swollen above, with an opening below the summit, 

 from which protrude many ciliated articulated arms. 



Shell. Composed of five testaceous oblong valves, two at the 



