MESOZOIC ERA: THE AGE OF REPTILES 



5*7 



two valves are alike. In some of these (Diceras, Fig. 491 F) each 

 valve is horn-shaped ; in others (Requienia, Fig. 491 /) one valve is 

 long and spirally twisted and the other flat, with a low spiral ; in 

 others (Radiolites, Fig. 491 G) one valve has the appearance of a cup 

 coral and the other is flat with prolongations extending into the 



Fig. 491. — Mesozoic pelecypods : A, Halobia (Daonella) lommeli (Triassic) ; B, 

 Trigonia clavellata (Jurassic) ; C, Gryphcea arcuata (Mesozoic) ; D, Inoceramus vanux- 

 emi (Upper Cretaceous) ; E, Aucella pioche (Lower Cretaceous) ; F, Diceras arietinum 

 (Jurassic) ; G, Radiolites cornu-pastoris (Upper Cretaceous) ; H, Eumicrotis curta 

 (Jurassic) ; /, Camptonectes bellistriatus (Jurassic) ; /, Requienia patagiata (Lower 

 Cretaceous). C, F, G, and / present forms very unlike the typical pelecypod. 

 CLELAND GEOL. — 34 



