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695 



TERTIARY FAUNA OF FLORIDA 



without radial striation, concentric sculpture inconspicuous ; right valve with 

 or without conspicuous radial and concentric sculpture, flat or concave. 



Subgenus Chlauiys Bolten, 1798. Type P. hlandicns Miill. 



Valves moderately inflated, subequal, in general similar (except in color) ; 

 sculpture of radial ribbing with or without Camptoncctes striation, with or 

 without an imbricate surface layer; frequently spinose on the ridges; ears 

 often discrepant, the posterior smaller. 

 Section Lyropecten Conrad, 1862. Type P. cstrellanus Conr. 



Shell resembling Pectcii s. s., but with both valves convex ; usually of 

 large size, heavy, and with radial striation and minute concentric imbrication; 

 ribs entire and not dichotomous ; valves equilateral. 

 Section Placopecien Verrill, 1897. Type P. Clintonius Say. 



Valves without ribs, the right smoother, the radial and concentric minor 

 sculpture of Lyropecten persisting; ears subequal; valves equilateral. 



Section Patinopccten Dall, 1898. Type P. caiiriniis Gld. 



Valves with small ribs, flat on the right valve and sometimes dichotomous ; 

 smaller and more rounded on the left valve ; concentric sculpture inconspicu- 

 ous ; radial striae absent or obsolete; ears subequal; valves nearly equilateral. 



To this group belong such fossil species as P. Meekii Conrad and P. 

 cxpansits Dall. 

 Section Nodipcden Dall, 1898. Type P. nodosns L. 



Shell like Lyropecten, but the ribs intermittently nodose, with more or 

 less prominent hollow nodes or bullae ; radial striation pronounced ; ears 

 unequal, the posterior smaller, the valves often more or less oblique ; imbricate 

 surface layer sometimes very marked. 



Section Cldauiys s. s. Type P. islandicus Miiller. 



Ribs small and numerous, imbricate or spinose ; valves subequal, similar, 

 oblique, or with unequal ears, the posterior smaller; Camptoncctes striation 

 and imbricate surface layer usually present; shell usually solid and opaque; 

 byssal notch and ctenolium present. 

 Section Aiqidpecten Fischer, 1887. Type P. operctdaris L. 



Shell thin, orbicular, with subequal inflated valves, usually equilateral, 

 with uniform, well-marked radial, not dichotomous, ribs and finely imbricate 

 radial striation ; ears subequal ; valves internally lirate on the edges of the 



