MARINE MOLLUSCA OP THE UNITED STATES. 101 



tending the entire length of the body-whorl ; inner lip simple ; columella 

 none ; outer lip acute. Bulla, Klein. 



Shell solid, cylindrical, involute ; spire none ; apex obtuse, umbilicated ; 

 aperture narrow and linear, as long as the body-whorl ; inner lip callous, 

 with a single anterior fold ; outer lip straight, simple. 



Cylichna, Loven. 



Shell rather thin, subcylindrical, imperforate, covered with an epidermis ; 

 spire distinct, apex obtuse, not mamillated, sutures simple, not carialicu- 

 lated ; aperture narrow behind, dilated and entire in front, nearly as long 

 as the body-whorl ; columella simple, not plicate ; outer lip straight, 

 acute. Utiuculus, Brown. 



Shell thin, hyaline, subumbilicated, inflated, ovate or subglobose ; spire 

 depressed, with a mamillated nucleus ; aperture expanded, not extending 

 beyond the body-whorl ; columella reflexed and sinuous ; outer lip sinu- 

 ous, produced anteriorly. Diapiiana, Brown. 



Shell ovate-pyriform, convolute ; spire distinct, depressed, somewhat con- 

 cealed ; aperture very wide, narrowed behind, entire and dilated in front ; 

 inner lip spirally convoluted as far as the commencement of the spire ; 

 outer lip simple, acute. Scaphander, Montfort. 



Shell concealed in the mantle, loosely convolute, thin, fragile, suborbicular 

 or ovate, striate or punctate ; spire small, often concealed ; aperture very 

 wide and open ; outer lip patulous. Phi line, Ascanias. 



Genus BULLA, Klein. 

 Ostracol, 82. 1753. 



The eyes are conspicuous, sessile on the middle of the frontal 

 disk ; mantle with the outer margin forming a thick fleshy lobe ; 

 foot with moderate lateral lobes partly investing the shell, the 

 hind part not extending beyond the shell. 



The species of this genus inhabit sandy mud-flats, the slimy 

 banks of river-months, and brackish places near the sea. They 

 feed on bivalves and other mollusks, which they swallow whole, 

 reducing and crushing them afterwards by the calcareous or horny 

 plates of 'their powerful, muscular gizzard. The shells are rather 

 solid, smooth, or nearly so, and marbled and mottled like birds' 

 eggs, or white. 



There are about fifty species, inhabiting temperate and tropical 

 seas, and ranging from low water to twenty-five fathoms. 



1. B. incincta, Mighels. 



Proc. Bost. Soc. Nat. Hist., i. 188. 1814. 

 Shell small, cylindrical, opaque, white; whorls three, the first 

 slightly depressed, the last distinctly girded above the middle ; 



