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69 s 



TERTIARY FAUNA OF FLORIDA 



without radial striation, concentric sculpture inconspicuous; right valve with 

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



Submenus Chlainys Tjoltcn, iJpS. Type /'. islandicus Miill. 



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

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

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

 often discrepant, the posterior smaller. 



Section Lyropccten Conrad, 1862. Type P. cstrellaints Conr. 



Shell resembling Pcctcn 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 Placopectcn Verrill, 1897. Type /'. Clintonins Say. 



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

 sculpture of Lyropccten persisting; ears subequal ; valves equilateral. 



Section Patinopcctcn Dall, 1898. Type P. caiiriiuts 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. Mcekii Conrad and P~. 

 c.\-/>ti>isns Dall. 



Section Nodipcctcn Dall, 1898. Type /'. nodosiis L. 



Shell like Lyropcctcu, 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 Chlainys s. s. Type P. islandicus Miiller. 



v^ 



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

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

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

 byssal notch and ctenolium present. 



Section .1 ; .tjiiipectcn Fischer, 1887. Type P. opcrcttlaris 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 



