480 



MOLLUSCA 



PHYLUM VI 



l)eak ; ligament as in Ghama. Shell structni-o like Caprina, but the free valve with 

 canals in the middle layer ; the walls of tlie canals bifurcate ontward, forming in 

 section a fringe of peripheral minor channels (Fig. 774, G). Cenomanian and Tiironian ; 

 Europe. 



Cajjrinula d'Orb. (Chaperia Mun.-Chalm.) (Figs. 775, 776). Right valve elongated, 



A attached, conical or incurved ; 



left smaller, gyrate ; both with 

 canal system, the periplieral 

 III i?P~7H/ Fc 'W^-x calials smaller ; hinge as in 



Caprina. 

 Turonian 

 gal, Sicily and Texas. 



IclbthtjosarcolitltusDcg- 

 marest {Gaprinclla d'Orl).) 



Caprmula haylei Gemm. 

 Upper Cretaceous ; Ad- 

 dauran, near Palermo, i/., 

 (after Gemmellaro). 



Cenomanian and 

 especially in Portu- 



Pio. 770. 



Caprlmda boissyi d'Orb. Cross- 

 section of the lower (.4) and upper 

 (_C) valves, c, Teeth ; s, Septum ; . 

 u, Body ca\'ity ; x, Sockets. 2/3 

 (after Woodward). 



Vir.. 777. 



Mass consisting of Caprotina 

 semiMriatd and C. stiiata 

 d'Orb., and a smooth Sphaeru- 

 lites. Greensand ; Le Mans, 

 Sarthe (after d'Orbigny). 



Cretaceous. Gaiirotina d'Orb. (Fig. 777). Canals obsolete, replaced in some species 

 by cavities. Neocomian to Turonian. 



Goralliochama White. Right valve conical, elongated, attached ; left smaller, with 

 incurved beak ; anterior cardinal tooth buttressed, strong ; posterior cardinal weak ; 

 canals as in Plagiop)tychus, bounded within by a coarsely cellular layer ; lower valve 

 with a prismatic outer and laminar inner layer, separated by an intermediate cellular 

 stratum. Cretaceous ; Califoinia. 



Superfamily 6. RUDISTACAE (Rudistae, Lamarck). 



Ghamacea in which the spirality of the valves has been lost, the area and ligament 

 vertically submerged, and the dorsal margins recurved over them so as to bring the ligament 

 into a sub-central position above the teeth but far below the dorsal margin, where it finally 

 becomes obsolete. The teeth, no longer forming a hinge but rather a clithrum, specially 

 modified for the vertical motion of the operculiform. left valve, in which rotation is prevented 

 by the projection of the modified teeth into deep sockets in the fixed valve ; the latter conical, 

 thick ; pallial line simple, enclosing the whole cavity ; shell structure specialised in tioo 

 very different layers; sessile, marine. 



The prisms of tlie outer shell layer are parallel to the long axis of the valve, and are cut 

 at right angles by numerous tabulae, which, together with the upper margin, often bear 

 impressions of radial vessels. The laminae of which the inner layer is composed are often 

 separated by cavities which recall the septa of Cyathopliylloid Corals, or those cavities found 

 in some oyster shells. In Ilippurites the outer layer is traversed by a complex of canals. 

 The Rudistacae are the most peculiarly modified of all Pelecypods. Their relationship to 

 the Chamidae through Monopleura and Ca'protina was first recognised by Quenstedt, and 

 afterwards confirmed by Woodward, Bayle, Zittel, Munier-Chalmas, Douville and others. 



