PLATE XIII. 



BOLUS CONRADI, HaLL. 

 Page 375. 



Fig. 1. View of the cast of the dorsal valve, showing the longitudinal septum and the filling of 

 the cavities beneath the margins of the transverse plate. 

 " 2. Cast of a ventral valve, showing the impression of the transverse plate, the median 

 depression of the hinge plate, and the cavities left by the teeth-like processes. 



Strophodonta profunda, Hall. 



Page 376. 



Fi6. 3. Impression of the surface of the concave valve of a small individual, with a portion of 

 the filling of the cavity between the valves, showing the impression of the ventral 

 valve on the margin. 

 " 4. Impression of the interior of the ventral valve of a large individual. The muscular 

 imprints in the figure are not represented so long as they are in the original 

 specimen. 



Spirifera eudora, Hall. 



Page 377. 



Fia. 5. Dorsal view of a specimen of this species. 

 " 7. Profile of the same specimen, showing the gibbosity of the valves, and the height 

 and curvature of the area. 



Spirifera gibbosa. Hall. 



Page-378. 



Fia. 6. View of a dorsal valve of this species. 

 " 8. Cardinal view of a specimen. 



Spirifera plwatella, var. radiata, Sowerbt. 



Page 378. 



Fig. 9. Dorsal view of a small individual, showing the extension of the lamellae in the dorsal 

 valve as seen in young specimens. 

 " 10. Ventral view of the same individual, showing the extent of the lamella in the ventral 



valve. 

 " 11. Profile of the specimen. 



Spirifera meta, Hall. 



Page 380. •< 



Fig. 12. Ventral view of a specimen. 

 " 13. Cardinal view of the same individual, showing the height and extent of the straight area. 



Spirifera nobilis, Hall. 



Page 380. 



Fig. 14. Dorsal view of an individual of medium size. 

 " 15. Ventral view of a specimen, showing plications in the mesial sinus. 

 " 16. Ventral view of a large individual. 

 " 17. Cardinal view of the specimen fig. 16. 



