CLASS I 



PELECYPODA 



479 



101, ^vith a posterior myophoric crest for the adihictor ; fixed valve conical or spiral, 

 cardinal formula 010; ligament in a deep groove, almost internal, parivincular, 

 opisthodetic. Cretaceous. 



G aprina ^'Orh. {Gemmellaria Muii.-Clialm. ; Cornucaprina Futt.) (Figs. 771, 772). 



Fig. 771. 



Loiif^dtudinal seetion of 

 the fixed valve of ('aprina 

 advcnu, showing cavitie.s in 

 tlie inner .shell layer. 



Fig. 772. 



Cross-section 

 of the free valve 

 of Caprina cam- 

 munis Qemmeh, 

 .showing parallel 

 canals in the 

 middle layer. 



Fig. 773. 



riwjidjityclius aiiuiUoni d'Orb. Upper Cretaceous ; 

 Gosau, Austria. 2/^. 



Very inequivalve, attached by the apex of the coniform right valve. Left valve large, 

 s]3irally twisted ; inner layer of lower valve made up of concentric lamellae between 

 which cavities are sometimes left. The middle layer of the free valve traversed by 

 numerous simple, wide, parallel canals, extending from the margin to the apex; tooth 

 of the attached valve Well developed, a series of depressions between the posterior 

 adductor scar and the margin. Cenomanian. The typical species, G. adversa d'Orb., 

 is of large size. 



Schiosia Buhm. Like Gaprina, but the fixed valve somewhat gyrate and the 

 canal system present in both valves. Cenomanian ; Upper Italy. 



Plagioptychus Math. (Sphaerocaprina Gemm. ; Orthoptychus Futt.) (Figs. 773, 



Fig. 774. 



Flaijioptychus ofjuiUoni (d'Orb.) (P. paradoxus Math.). Upper Cretaceous (Hippurites Limestone); Le 

 Beausset, Var, France. A, Right. B, Left valve of the same individual, seen from within, 2/3. a, Anterior; 

 a' Posterior adductor scar ; I, Ligamentary groove ; c, Anterior tooth ; c'. Posterior tooth of left valve ; 

 f?,' Socket; », Buttress. C, Section of the small valve near the margin, showing canals (y) of tlie middle layer. 

 JIagnified. 



774). Right valve conical or twisted, attached ; left valve convex, with incurved 



