182 LUCAPINA-MEGATEBENNUS. 



stages of growth ; internal callus-rim of perforation somewhat ex- 

 cavated posteriorly in young shells. 



Animal black, " like India-rubber," the finely granulose mantle 

 covering the shell in life, its edges smooth, thinned, not papillose ; 

 border of dorsal pore simple, not papillose. Foot (in alcoholic spec- 

 imens) extending posteriorly a short distance beyond mantle, encir- 

 cled by a row of short papillae borne on a low epipodial ridge. Ten- 

 tacles long, pointed, clavate, eyes on prominent rounded peduncles 

 behind them. 



L. CRENULATA Sowerby. PI. 44, figs. 95, 96. 



Shell very large, light buff or stained with grayish, the surface 



radiately striate, obscurely decussated by growth-lines and wrinkles. 



Edge very regularly and finely serrated ; interior white ; muscle- 



' scar broad, not impressed. Perforation large, oval, a little in front 



of the middle. Length 120, breadth 78, alt. 23 mill. 



Monterey to San Diego, Cat. 



Fissurella crenulata SOWB. Catal. Tankerville, Appendix, p. vi, 

 1825 ; Conchol. Illust., f. 31. REEVE, Gonchol. Icon., f. 18. La- 

 capina crenulata of Carpenter and others. Megathura California 



NUTTALL MSS. 



For account of animal and dentition see Dall, Amer. Journ. 

 Conch. 1872, p. 131. 



This is the largest of the Fissurellidse, and in its great size and 

 beautifully crenulated border is one of the most distinct. 



See under Glyphis for certain points in which some species of that 

 genus and this seem to approach. 



Genus MEGATEBENNUS Pilsbry, 1890. 



The small species grouped under this name agree with Fissurellidea 

 (as restricted to Orbigny's type) in having a partially internal, large- 

 apertured shell, a mantle ample enough to cover the entire dorsal 

 surface of the foot and head, its edges entire ; they differ from 

 Fissurellidea in the much greater proportional size of the shell, more 

 elevated body, the foot (viewed ventrally) almost as extensive as the 

 mantle, the margin of the latter not at all thickened, and the shell 

 not white-bordered above. 



F. bimaculata Dall may be considered the type. 



In the specimen examined by me, the very densely and minutely 

 granulate mantle envelopes the entire head and upper surface of the 



