broad, flat, thin, and stands obliquely to the side of the 
chell. %. Cornwall. 
Grnus.—BULL/A. 
Extremely thin, somewhat involute on one side, and 
destitute of a columella or spire; aperture large 
and expanded. 
B. Averta. Lam.— Butta A. Inn. 1183.—Sow. G. 
SF. 1—D. p. 477.—Ch. f. 1354,5.—Don. t. 220.— 
Mont. p. 208. vig. 2. f. 1.3.—Da. Cos. €: 2. f. 3.— 
Suborbicular, thin, glossy, pellucid, brittle, white, 
slightly wrinkled, no external convolution or umbi- 
lieus ; inner lip very small, slightly involuted, visible 
to the end ; aperture occupying nearly the whole of the 
shell. 0,70. Devonshire, Kent, &c., common. 
B. Punorata. Clark. Z. J. 3. p. 339.—Buria P. 
Adams. Ian. T.2. ¢ 1. f. 6,8.—F. p. 294,—Ovate- 
oblong, extremely thin, white, pellucid, glossy, marked 
with transverse dotted lines; inner margin arcuated 5 
apex obtuse with a very shallow umbilicus. 0,10. 
Exmouth and Torquay in pools at the lowest spring 
tide, very rare. 
8B. Prurnosa. Clark. in Z. J. 3. p. 339.—Sub- 
globose, subopaque, dead frosted white, delicately 
