PLATE VI. 



Page 

 Figs. 1 to lb. Spirifer boonensis ? 381 



A young typical specimen belonging to this species. 



Fig. 1. Dorsal view. 



la. Ventral view. 



lb. Side view. 



Hermosa formation: Bear Creek, Durango quadrangle (station 2214). 



Figs. 2 .\nd 2a. Spirifer boonensis ? 381 



A mature but imperfect example of this species. This is a large shell, but represented 



by the figures which are somewhat enlarged as out of proportion with the preceding 



illustrations. 



Fig. 2. Dorsal view. 



2a. Side view. 



Hermosa formation: Bear Creek, Durango quadrangle (station 2214). 



Fig. 3. Spirifer boonensis? 381 



A ventral valve embedded in rock, which may perhaps belong to this species. It comes 



from a higher horizon in the Hermosa formation than the typical form shown by figs. 



1 and 2. 



Specimen seen from above. 



Hermosa formation: South fork of Hermosa Creek, Durango quadrangle (station 2201). 



Figs. 4 and 4a. Spirifer rockymontanus 383 



A large specimen belonging to this species. 



Fig. 4. Dorsal view. 



4a. Side view. 



Weber shale; South of head of Empire Gulch, Leadville district (station 2267). 



Figs. 5 and 5a. Spirifer rockymontanus - 383 



A somewhat smaller specimen than the foregoing, in which the median furrow on the 



fold is larger and stronger than the lateral ones. 



Fig. 5. Dorsal view. 



5a. Side view. 



Weber shale: South of head of Empire Gulch, Leadville district (station 2267). 



Figs. 6 and 6a. Spirifer rockymontanus 383 



A smaller but very characteristic individual, in which the fold is numerously plicated. 



Fig. 6. Dorsal view. 



6a. Side view. 



Hermosa formation: Near southern edge of Engineer Mountain quadrangle (station 2249). 



500 



