32 CONC HOLOGY. 
B. perforatus. B. sulcatus. 
B. rugosus. B. cylindraceus. 
B. latus. B. ovularis. 
B. plicatus. B. radiatus. 
B. galeatus. B. fistulosus. 
B. spinosus. B. Lyonsii. F 
B. placianus. 
B. tintinabulus.* B. miser.* 
B. geniculatus.* 
4, Genus JAcasta. Pl. V. 
Animal. Body without a peduncle, and inclosed in a multi- 
valve shell, found in sponge or marine bodies, mouth and tenta- 
cula placed in the apex, or upper part of the body. 
Shell, Patella-shaped, sub-conically oval, formed of six lateral 
unequal valves forming the base, which being convex prevents 
the shell from standing by itself in an erect position, when de- 
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. Pl. 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 microscopic, and found only in the 
seas of hot countries. Inhabits the China seas. Three species. 
Creusia stromia. Creusia spinulosa. 
C. verruca. 
6. Genus Pyrgoma.- Pl. V. 
Animal. <As above. 
