32 CONCHOLOGY. 



tached from the substance which envelopes it. Inhabits the Bri- 

 tish seas. Four species. 



Acasta montaguii. Acasta glans. 



A. sulcata. A. tubulosa. 



5. Genus Creusia. PI. V. 

 Animal. Body, subglobular, inclosed in an operculated shell ; 

 having three or four pairs of tentacular arms : mouth at the 

 anterior part of the body. 



Shell. Sessile, fixed, orbicular, conical, consisting of four 



united unequal valves ; attached to madrepore and other marine 



substances, they are almost microspopic, and found only in the 



seas of hot countries. Inhabits the China seas. Three species. 



Creusia stromia. Creusia spinulosa. 



C. verruca. 



6. Genus Pyrgoma. PI. V. 

 Animal. As above. 



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

 above ; apex perforated ; aperture small, elliptical, operculum 

 quadrivalve. Inhabits the Indian seas. One species. 

 Pyrgonia 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 Isevis, Anatifera dentata. 



A. villosa. A. striata. 



A. vitrea. A. Aculeata. 



