MAZATLAN UNIVALVES 213 
Hab.—Mazatlan ; eregarious, often adhering to each other, not 
common; L’pool Col. 
Tablet 1017 contains 3 sp. finely grown.—1018, 3 do. usual 
state.—1019, 3 do. irregularly grown.—1020, 6 sp.; one ‘with 
5 corners, another with 4, another with 3, another with 2, 
another with 1, the other circular.—1021, 2 sp. very deformed 
growth.—1022, 2 do., one with double margin, the other ex- 
tremely depressed.—1023, 1 sp. with dead Balani, enclosing a 
Crustacean. 
Famity FISSURELLIDZ:. 
Genus FISSURELLA, Brug. 
The Mazatlan Fissurelle naturally divide themselves into 
two sections; the first with the surface irregular, and the 
margin not crenulated except by the projecting ribs; the 
second with the surface cancellated, the margin crenulated, 
the apex in the young sbell prominent and recurved, the 
callus frequently truncated, sometimes laminated. In the first, 
the Rimuloid stage must be of very short duration, as extremely 
young shells were found, of the same form as the adult: in the 
second, this stage continues for a comparatively long period, 
as may be observed in the English species, as well as in the 
specimens here recorded. To the latter group H. & A. Adams 
(Gen. 1. 447) have unfortunately given the name of Lucapina, 
as of Gray. The animal however of Gray’s typical species, L. 
crenulata (Fig. Moll. An. p. 92, no. 159), is described by 
Nuttall as like that of Parmaphorus, extremely large, and 
completely enveloping the shell.—The shape and markings, 
which in most species are tolerably constant, are in others very 
variable: even the form of the aperture and callus is in some 
instances remarkably changeable. 
Section A. Margin interrupted by ribs. 
271. FissuRELLA VIRESCENS, Sow. 
Proc. Zool. Soc. 1834, p. 125.—MWiill. Syn. Nov. Test. Viv. 
p. 154.—Sow. Conch. Til. sp. 31, f. 37 (quasi F. coarctata, 
King.)—Rve. Conch. Ic. pl. 4, f. 12, sp. 12—Mke. Zeit. f- 
Mal. 1851, p. 36, no. 130.—C. B. Ad. Pan. Shells, p. 238, 
no. 361.—H. & A, Ad. Gen. i. 446. 
