Descriptions of Devoxiax Fossils. 237 



resembles the S. ■uieqmsfj'f(ff<i Conr., except, pei'lia])s, in tlio narrower 

 area. The interior ciuiracters show it to be uf a ditferent type. 



Formation and local'dij. In the marly beds at Rocktbrd and Ilack- 

 berry, Iowa, 



Genus — SPIRIFERA Sow. 

 Spikifeka Okestes n. sj?. 



Plate 11, flgs. lft-20. 



Shell smaller than medium, somewhat wider than long, and usually a 

 little gibbous, frequently extended on the hinge-line in larger specimens, 

 but with hinge extremities rounded in young and smaller individuals. 

 Yalves marked by moderately strong, rounded or slightly angular 

 plications, simple on the sides of the shell, but bifurcating on the mesial 

 fold and sinus, where there are from four to six plications. Mesial 

 fold strongly elevated in front on large specimens. Yentral area mod- 

 erately high, strongly incurved near the beak ; foramen rather large. 

 Surface marked by very line striae parallel to the plications. 



This species difters from its associate, 8. Whitneyi {=^ 8. Yemeuilii ), 

 in the much stronger and more angular plications, in the sharper eleva- 

 tion and angular aspect of the mesial fold and sinus, in the higher 

 cardinal area, and in having the plications of the mesial fold and sinus 

 stronger than those of the body of the shell, while in that species they 

 are always smaller. 



Foi'matiori and locality. In the marly beds at Rockford and Hack- 

 berry, Iowa. 



Spikifera subvaricosa n. sjp. 



Plate 11, flgs. 12-15. 



Shell small, seldom more than five-eighths of an inch on the hinge- 

 line. Yalves highly convex, the ventral somewhat gil)bous, with an 

 incurved cardinal area of moderate height, divided by a triangular fora- 

 men which is higher than wide ; cardinal angles slightly rounded, 

 plications subangular, eight to ten on each side of the ventral \alve, 

 with one moderately strong in the bottom of the sinus not always 

 extending to the apex ; on the dorsal valve the mesial fold consists of 

 two strong equal plications, with a deep angular groove between. Sur- 

 face marked by somewhat strong, rugose, ziz-zag lines of growth which 

 are sharply bent backward as 'they cross the plications. 



This species resembles 8. varicosa Hall, of the Upper Helderberg 

 limestones of iSTew York and Indiana ; but it differs by its shorter form, 

 more curving area, and duplicate character of the mesial fold. 



Formation and locality. In the limestone below the village of 

 Waterloo, Iowa. 



