480 



MOLLUSCA 



PHYLUM VI 



beak ; ligament as in Ghama. Shell structiire like Gaprina, biit tlie free valve with 

 canals in the luiddle layer ; tlie walls of the canals bifurcate outwarcl, forming in 

 section a fringe of periplieral minor cliannels (Fig. 774, (7). Cenomanian and Turonian ; 

 Europe. 



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



A attaclied, conical or incurved ; 



left snialler, gyrate ; botli with 

 caiial System, the periplieral 

 canals smaller ; hinge as in 

 Gaprina. Cenomanian and 

 Turonian, especially in Portu- 

 gal, Sicily and Texas. 



Ichthyosarcolithus Des- 

 marest {Gaprinella d'Orb.). 



Fig. '775. 



Caprinula haylei Geinm. 

 Upper Cretaceous ; Ad- 

 dauran, near Palermo. 1/2 

 (after Gemmellaro). 



Fig. 776. 



Caprinula boissyi d'Orb. Cross- 

 section of the lower(^)and upper 

 {B) valves. c, Teeth ; s, Septum ; 

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

 (after Wood ward). 



Fig. 777. 



Mass consisting of Caprotina 

 semistriata and C. striata 

 d'Orb., and a smooth Spliaeru- 

 litcs. Greensand ; Le Mans, 

 Sarthe (after d'Orbigny). 



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

 by cavities. Neocomian to Turonian. 



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

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

 canals as in Plagioptychus, bounded within by a coarsely cellular layer ; lower valve 

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

 Stratum. Cretaceous ; California. 



Superfamily 6. RUDISTACAE (Rudistae, Lamarck). 



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

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

 into a sub-central position above the teeth but far beloio the dorsal margin, where itfinally 

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

 modißedfor the vertical motion of the operculiform, left valve, in which rotation isprevented 

 by the protection of the modißed teeth into deey sockets in thefixed valve ; the latter conical, 

 thich ; pallial line simple, enclosing the whole cavity ; shell structure specialised in two 

 very different layers ; sessile, marine. 



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

 at right angles by numerous tahulae, which, together with the upper margin, often hear 

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

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

 in some oyster shell s. In Hippurites the outer layer is traversed by a complex of canals. 

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

 the Chaniidae through Monopleura and Caprotina was first recognised by C^uenstedt, and 

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



