EXPLANATION OF PLATE IV. 



Paga 

 SXREPTOKHYKCnOS INEQU^LIS 252 



Fig. 1. View of a dorsal valve, showing an nnusual breadth, from Ogden Canon. 



2. View of a narrower ventral valve, showing finer and more even stria;, from Logan 

 Canon. 



Steeptoriiynciius inflatds 253 



Fig. 3. View of a very rotund, dorsal valve, with fine, even-strise, from Dry Caflon. 



Stkopiiomena ehomboidalis 253 



Fig. 4. View of a specimen from Dry Canon, showing fine, even wrinkles. 



Spirifera centronata , 254 



Fig. 5. View of a large dorsal valve, showing the usual features of the species, Dry Canon. 

 6. A smaller ventral valve, from the same locality. 



Spirifera Alba-pinensis 255 



Fig. 7. View of a ventral valve, from a siliceous layer at White Pine, Nevada, as obtained 

 by gutta-percha cast from the matrix. 

 8. Another ventral valve, from Logan CaQon, Utah. 



• CnONETES LOGANENSIS 253 



Fig. 9. View of the specimen described. 



Athyris planosulcata ? 2.j7 



Fig. 10. View of a small ventral valve from Logan Canon. 



11. A partial cast of another ventral valve from Cottonwood Canon, Utah. 



Ehynchonella pustulosa? 257 



Figs. 12-13. Dorsal and front views of a specimen from Dry CaQon, Utah. Enlarged. 

 14. Dorsal view of the specimen, natural size. 



Athyris Claytoni 256 



Figs. 15-17. Dorsal profile and ventral views of a specimen of the species, showing the form of 

 shell and the perforation of the beak. 



Terebratula Utah 258 



Fig. 18. View of a ventral valve, natural size. 



Michelina sp. ? 251 



Fig. 19. View of the specimen referred to under the description. 



