SPIRIFER^ OF THE UPPER HELDERBERG GROUP. 211 



Figures 14, 15, 16 and 17 of Plate 31 represent the characteristic features of this spe- 

 cies from the localites cited below. 



Figure 18 is a ventral valve with the dorsal valve removed, except at the apex, and 

 showing the disposition of the crura and spiral arms. 



Figure 19 is a cardinal view of a smaller individual. 



Geological formation and localities. In the limestone of the age of the Upper 

 Helderberg group, at Columbus, Ohio ; Falls of the Ohio (Louisville and Jeffer- 

 sonville), and at Charleston landing, Indiana. 



Spirifera euniteines, var. fornacula. 



PLATE XXXI (figures 11, 12 and 13). 



Sp:riftr fornacula : Hall, Tenth Report on State Cabinet, p. 164. 1857. 

 " " Description of New Pal. Fossils, p. 114. 1857. 



This species possesses the essential characters of 8. euruteines, with the area a 

 little more arcuate in the upper part ; while the relative strength of the plications 

 offer no characters of specific importance : there are, in one specimen, nine, and 

 in another ten, in the space occupied by eight plications in S. euruteines proper. 



In casts of this variety, the mesial fold is flattened on the summit and grooved 

 towards the upper part, and the sinus is more distinctly flattened on the bottom. 

 In one specimen the cardinal angles are produced and mucronate ; but this may 

 likewise occur from the different surrounding conditions. 



The figures 11, 12 and 13 are representations from a specimen heretofore de- 

 scribed under the name oi 8. fornacula. 



Geological formation and locality. This form occurs in limestone of the age of 

 Ihe Hamilton group, and perhaps also in Comiferous limestone, at the Bake-oven, 

 on the Mi-ssissippi river, Illinois. 



Spirifera nianni. 



PLATE XXXI. 

 Spiriftr manni .- Haii in Tenth Report on tlie State Cabinet, p. 128. 1867. 



Shell semielliptical or subquadrate ; valves very unequally convex : 

 hinge-line equal to the greatest width of the shell ; cardinal extremi- 

 ties angular, and sometimes produced in acute extensions. 



Ventral valve subpyramidal, the height often nearly equal to two-thirds 

 the length ; greatest elevation at the apex, and thence curving to the 

 front and lateral margins ; mesial sinus angular above, and rounded or 



