﻿109 Paleontology 3 1 



shell in some specimens. A pair of dental lamellas extend across 

 the umbonal cavity. 



Dorsal valve comparatively flat but rounding off toward the 

 lateral extremities and the hinge line. A broad, median fold 

 which is depressed to or slightly below the level of the sides of the 

 valve is present. It is limited by a shallow groove on either side 

 and tapers to a point at the umbone. Etched specimens show 

 laterally directed spiralia consisting of three or four coils. 



This species shows but little likeness to any other species of the 

 genus Spirifer in which it is placed provisionally. Externally 

 it has some resemblance to the species of Metaplasia in the in- 

 equality of the valves and small number of plications. The 

 presence of dental plated, however, bars it from this genus. 



Spirifer utahensis Meek. 



PI. II figS. 2-2C. 



Comparison with Meek's types shows unquestionable identity 

 of the Montana forms with the Nevada species, although such 

 identity is not altogether evident from Meek's description. In 

 Meek's specimens the striae on the fold and sinus are less than 

 eight (his minimum number) in all but the largest specimen. 

 Only two of the types show clearly the character of the fold, and 

 in these it differs materially in development. In the Montana 

 collection, which numbers 40 or 50 specimens, the fold is rather 

 variable. In some specimens it is elevated above the adjacent 

 portion of the shell barely enough to be recognizable except at 

 the anterior margin. Generally, however, it is moderately 

 prominent from the beak to the front. The sinus, though 

 generally more prominent than the fold, is in a few specimens 

 extremely shallow. The striae on the fold and sinus range in 

 number from four to nine. The striae marking the surface of 

 each valve do not in general exceed 35 in number. 



This is one of the most abundant species in the Montana fauna. 



Locality. — Princeton, Montana. 



