MAZATLAN UNIVALVES 213 



Hob. Mazatlan ; gregarious, 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. 



FAMILY FISSUEELLID^E, 



GENUS FISSUBELLA, Brug. 



The Mazatlan Fissurellse 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 shell prominent and recurved, the 

 callus frequently truncated, sometimes laminated. In the first, 

 the Bimuloid 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. i. 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 ly ribs. 



\ 271. FlSSURELLA VIEESCENS, Sow. 



-r 



Proc. ZooL Soc. 1834, p. 125. Mull. Syn. Nov. Test. Viv. 

 p. 154. Sow. Condi. III. sp. 31, f. 37 (quasi F. coarctata, 

 Klng.)Rve. Condi. Ic. pi. 4, f. 12, sp. 12. Wee. Zeit. f. 

 Mai. 1851, p. 36, no. 130. C. B. Ad. Pan.. Shells, p. 238, 

 no. 361. H. & A. Ad. Gen. i. 446. 



