GENUS XXII. BULLA. 103 



very various ; the B. Ocum and verrucosa differ but little from 

 the Cyp'cea, scarcely in any thing but in the teeth being want- 

 ing on one lip. The B. Volva, birostris, Spelta, gibbosa, &c. 

 gradually approach to the form of the Cyprcea, but have no 

 teeth on either lip. B. Naucum, aperta (f. G2), Hydtitis, 

 Ampulla (/". 65), Ugnaria, P/iysis, Amplustra, &c. are some- 

 what globular in shape, with a large aperture, and the edge 

 of the outer lip very thin and acute ; these may perhaps be 

 considered as the true Bulla, but even these differ considerably 

 from one another. 



B. Ficus (/. 64), Rapa, and those with the straight canal, 

 which is the essential character of the Murex, Avould seem to 

 arrange better in that genus, where indeed Linnaeus had placed 

 them in his Musceum Liudovicce IJlricce. 



B. fontinalis, hypnorum, achatina, &c. agree with many 

 species of the Helix. 



B. Terebellum (J". Q>3^ seems more like a Cone ; Linnaeus 

 remarks that it has the aperture of a Cone. 



What is known of the animals inhabiting these shells proves 

 only the great variety there is among them, and the impro- 

 priety of classing them together. The animals of J3. aperta, Ug- 

 naria (see pi. 1 1./. 16), Hydatis, &c., and probably of several 

 others, are much larger than the shell, and appear like MoUusca, 

 having the sliell concealed under the skin, somewhat similar 

 to the shield of the Laplisia ; these have no tentacula, but two 

 small eyes on the top of the head, and a curious structure of a 



