CEETACEOUS PERIOD. 



461 



subcylindrical, tapering cavity, having one or more projecting ridges 

 on the sides, running the whole length. Some foreign Cretaceous 



Figs. 832-837. 



Coxchifers. — Fig. 832, Exogyra arietina ; 833, Ostrea larva ; 834, Exogyra costata ; 835, Gryphsea 

 vesicularis ; 836, G. Pitcheri ; 837, Inocerauius probleniaticus. 



species are figured on page 462; Fig. 862 a shows the interior of one: 

 there are two prominent ridges, but one is only partly free in the in- 



Figs. 838-843. 

 8436 



Gasteropods.— Fig. 838, Pyrifusus Newberryi; 839, Fasciolaria buccinoides ; 840, Anchura 

 (Drepanocheilus ) Americana ; 841, Margarita Nebrascensis ; S42, Nerinsea Texana ; 843 a, b, Bulla 

 speciosa. 



