FOSSILS OF THE CAEBOMFEEOUS. 



217 



upper lateral slopes of the valve ; area beneath the beak unknown, as it is 

 concealed by the adhering matrix. Dorsal valve nearly as convex as the 

 ventral ; beak small, incurved, and projecting a little over the hinge margin; 

 mesial lobe elevated, about as broad as the sinus of the opposite valve and 

 with a slight median groove; lateral ribs, four on each side. 



Surface of valves marked by fine concentric lines of growth. 



This species is allied to S. Leidyi, but differs in the less number of ribs 

 on the valves, and also in the rounded lateral angles. 



Formation and locality. Lower portion of the Carboniferous Group, 

 Richmond Mountain, Eureka District, Nevada. 



\ 



Spirifera ueglecta Ball. 

 Plate xviii, fig. 10. 



Spirifer neglectus Hall, 1858. Geol. Surv. Iowa, vol. i, pt. 2, p. 643, pi. xx, fig. 5. 



neglectus Worthen & Meek, 1875. Geol. Surv. Illinois, vol. vi, p. 523, pi. xxx, 

 figs. Ic, 2 a. 



This large and strongly-marked species of the Keokuk limestone of the 

 Lower Carboniferous of Iowa and Illinois, is represented by single valves 

 and one medium-sized entire shell. There appears to be a strong specific 

 identity between the Nevada specimens and those from the Mississippi 

 Valley. 



Formation and localities. Lower portion of the Carboniferous Group, 

 Richmond Mountain, and on the east slope of a small conical hill on the 

 east side of Secret-canon-road Canon, Eureka District, Nevada. 



Spirifera desiderata, n. sp. 

 Plate vii, fig. 8. 



Dorsal valve subsemicircular in outline, extremities submucronate, 

 moderately convex ; mesial fold not very prominent and flattened across 

 the top, well defined at the margins, and with a slightly depressed median 

 line. 



Surface marked by about thirty simple rounded plications, which are of 

 moderate strength and little elevated ; a few concentric lines are shown, but 



