EXPLANATION OF PLATE IV. 



rage. 

 STRKI'TOKIIYNCnCS INUQIIALIS 'i^i 



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



2. View of a narrower ventral valve, showing finer and more even strise, from Logau 

 Canon. 



STREPTOIinVNCIIUS INFLATUS 253 



Fig. 3. View of a very rotnud, dorsal valve, with fine, even stri;e, from Dry Cafion. 



SmOPUOMENA RHOMBOIDALIS ioi 



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



Spirifeba centronata 254 



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

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



Spirifera Alba-pinensis 2.55 



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 CiiFion, Utah. 



Chonf-tes Loganensis 2.5.3 



Fig. 9. View of the specimen described. 



Athyris planosulcata ? 2.57 



Fig. 10. View of a small ventral v.alve from Logan Canon. 



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



RUVNCHONELLA PUSTHLOSA ? 257 



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

 14. Dorsal view of the specimen, natural size. 



Athyris Claytom '-'56 



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. 



Terebratui-a 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. 



