FOSSILS OF THE LOWER OAKBONIFEROUS. '269 



a little finer and more even than on the other ; but the differences are even 

 less than occur among specimens of P. elegans from the typical locality. 



Formation and locality. — In limestone of Lower Carboniferous age, north 

 of Snowstorm Hill, near Dry Canon, Oquirrh Mountains, Utah. Collected 

 by J. E. Clayton. 



Genus SPIRIFERA Sowerby. 

 Spirifera striata. 



Plate V, figs. 13-15. 

 Anomites striatus Martin ; Spirifer striatus Sowerby and others. 



Shell rather above the medium size, transversely oval or semi-elliptical, 

 the hinge-extremities either rounded or slightly extended beyond the width 

 of the shell below. Valves moderately convex, or in some cases rather 

 strongly rounded; the ventral valve most rotund and marked by a broad 

 mesial depression, the margins of which are not strongly defined ; front of 

 the valve in the depression somewhat extended and bent upward; beak 

 small, pointed, and closely incurved ; area small, poorly defined, the mar- 

 gins rounding to the body of the shell. Dorsal valve most ventricose in 

 the upper part ; the sides gradually sloping to the margins, and the center 

 strongly elevated, forming a distinct, sharply rounded mesial fold, which is 

 narrow in the upper part but expands very rapidly as it approaches the 

 front of the shell. 



Surface of the valves marked by moderately strong, radiating plica- 

 tions, which are distinct and subangular on the upper j)art of the shell, but 

 frequently bifurcate and become flattened toward the margin, often forming 

 fascicles of three, four, or more on the extension of the valves, while those 

 near the middle are usually in pairs, but not uncommonly simple. 



The species is extremely variable in form and surface-markings as it 

 occurs in the collections examined, representing two quite distinct types, 

 which appear to characterize two different horizons of the geological section 

 of the district in which they were found. Although these differences are 

 easily detected on close examination, still they are not sufficiently strong 

 and marked to be considered as of specific or even varietal importance, 

 and, in their extremes, are not nearly so great as those ascribed to the species 



