PLATE XIV— Continued. 

 Genus Cythfaiodok. 



Fig. 19. View of the right side of an internal cast of G. tumidus, showing the muscu 

 lar impressions and pallial line. From the Upper Helderberg limestone. 

 Columbus, Ohio. 



" 20. Exterior of a left valve of C. appresms (= Nuculites appressus Conrad), 

 showing the usual form of the shell. 



" 21, View of the interior of the cardinal border of the two valves in Jaxtaposition, 

 as obtained by a gutta-percha cast from the natural mold of the interior 

 (the right valve being apparent), showing the interlocking of the cardinal 

 teeth, of which there appear to be four in the right and five in the left 

 valve. Hamilton group. Hardy county, Virginia. 



