402 



MOLLUSCA 



SUB-KINGDOM VI 



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

 spirally twisted ; inner layer of lower valve made up of concentric lamellae between 



FIG. 725. 



Plagioptynhus Aguilloni, d'Orb. (P. Coquandi, 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 ; 

 (I, Socket ; s, Buttress. C, Section of the small valve near the margin, showing canals (y) of the middle layer. 

 Magnified. 



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 depres- 

 sions between the posterior 

 adductor scar and the margin. 

 Cenomanian. The typical 

 species, 0. adversa, d'Orb., is 

 of large size. 



Schiosia, Bohm. Like 

 Caprina, but the fixed valve 



FIG. 726. 



Caprinula Baylei, Gem in. 

 Upper Cretaceous ; Ad- 

 dauran, near Palermo. 1 /-_> 

 (after Gemmellaro). 



FIG. 727. 



Caprinula Boissyi, d'Orb. Cross- 

 section of the lower (A) and upper 

 (B) valves, c, Teeth ; s, Septum ; 

 u, Body cavity ; x, Sockets. 2/ 3 

 (after Woodward). 



FIG. 728. 



Mass consisting of Crij>r- 

 tina semist riata and C. striata, 

 d'Orb., and a smooth Sphaeru- 

 lites. Greensand ; Le Mans 

 (after d'Orbigny). 



somewhat gyrate and the canal system present in both valves. Cenomanian ; Upper 

 Italy. 



Plagioptychus, Math. (Sphaerucaprina, Gemm. ; Orthoptychus, Futt.), (Figs. 724, 



