FOSSILS OF THE SILUEIAN AND DEVONIAN ROCKS. 



Roemer's species is very rare in Germany, making it difficult to procure speci- 

 mens showing the exact features of perfect shells. From these facts we must 

 draw the conclusion that both species are either identical, or that one is only 

 a variety of the other. In this case Mr. Conrad's species has the priority over 

 Roemer's and Spir. acuminata would be maintained, even if its similarity with 

 Sp. cultrijugatax were admitted. Figures 7 and 8, plate 8, show a very fine 

 internal cast of this species. 



Formation and Locality. Pound abundantly and in good condition in the Devonian limestone of 

 Kentucky and Indiana, around the Falls of the Ohio. 



Spirifera atwaterana. s. A. MILLER. 



Plate IX., figures 1 to 7. 

 Spirifer pennatus and Spirifer ligus. Owen. Geol. Kep. of Wisconsin, Iowa and Minnesota, p. 585, pi. 



III., figs. 3, 4 and 81852. 



Spirifer pennatus, Hall. Geology of Iowa, Vol. I., Part II., p. 510, pi. 5 1858. 

 Spirifer ativaterana, S. A. Miller. Proc. Davenport Acad. Sci. 1878. 



This species is generally known under the name of Spir. pennata ; but this 

 specific designation was used already in 1820 by Atwater for another Spirifera, 

 and, therefore, another name had to be adopted for this shell. S. A. Miller, 

 Esq., of Cincinnati, Ohio, named it atwaterana. 



This species belongs to the large sized Spirifera ; in width it is not exceeded 

 by any other kind ; it is very variable in form, from sub-globose to transverse 

 and broadly triangular semi-circular, or semi-elliptical, sometimes inequi- 

 lateral ; hinge-line always more or less extended into wing-like expansions, 

 resembling in this feature Spir. mucronata ; valves mostly equally convex. 



Ventral valve most convex in the middle and on the umbo ; beak much 

 elevated above the hinge-line, more or less pointed and slightly incurved. 

 Mesial sinus [strongly defined at margins, rapidly widening towards base, and 

 produced in an angular extension in front. Area large and extending to cardi- 

 nal extremities^; concave and striated vertically and longitudinally ; foramen 

 large and open to apex, and forming an equilateral triangle. 



Dorsal valve also most gibbous in the middle and on the umbo ; beak mark- 

 edly incurved ; valve curves from the point of the greatest convexity regularly 

 to anterior and lateral margins, and is more or less compressed at cardinal 

 angles ; mesial fold is strongly elevated, sometimes a little flattened on top, 

 and often sub angular towards front. 



Surface marked by from fifteen to twenty-five, or even more simple, rounded 

 plications on each side of mesial fold and sinus ; central ribs are much stronger 

 than lateral ones ; of the former only about six to eight on each side reach 

 apex, all others run out on the margins of the cardinal area. In well preserved 



