﻿32 Bulletin 20 110 



Spirifer englemanni Meek. 

 PI. II figs. 3 - 3 b. 



Shell subhemispheric in outline. Valves unequal, the dorsal 

 valve moderately convex, the central valve greatly elevated in 

 the umbonal region. Surface of shell marked by 14 to 20 radiat- 

 ing rounded plications. The entire surface is covered by very 

 fine radiating striae. These finer markings are generally absent 

 through exfoliation, but three or four of the Montana specimens 

 show them distinctly. They are also well preserved in specimens 

 from the Eureka district, Nevada, identified by C. D. Walcott. 



Ventral valve with a very high area inclined slightly backward 

 near the beak, which is small and pointed and slightly incurved. 

 A rather broad and shallow sinus extends from the beak to the 

 front. Dorsal valve with rather low fold. 



The only notable differences observed between the specimens 

 described and the types are the height and backward curvature 

 of the area of the ventral valve. In the types the latter feature 

 exceeds the curvature seen in the Montana specimens, but the 

 height is less. These differences, however, are not believed to be 

 of specific value. 



Locality. — Princeton, Montana. 



Spirifer cf. argentarius Meek. 

 PI. II figs. 4~4a. 

 Some small shells with nonplicated fold and sinus are referred 

 to this species. One specimen shows traces of somewhat 

 lamellose concentric strias, which, together with the greater 

 prominence and coarseness of the lateral striae and less elevated 

 area, distinguish it from Sp. engelmanni. 

 Locality. — Princeton, Montana. 



Spirifer disjunctus var. animasensis Girty. 



This form, which is distinguished from Sp. disjunctus by the 



high area and subpyramidal form and slightly twisted beak is 



present only in the Utah collections. Sp. disjunctus , which is so 



common in the Threeforks shale above the Jefferson limestone, 



