No. 109.] 131 



Spirifee segmentus ( n. s.). 



Pal. N.Y. Vol. iv. 



Shell transversely semioval, less than half as long as broad • hinge 

 equalling the greatest width of the shell, terminating in salient 

 angles : dorsal valve depressed -convex ; beak projecting slight- 

 ly beyond the hinge, scarcely incurved ; mesial fold narrow 

 depressed and rounded, not plicated : ventral valve the more 

 convex, most prominent at the beak, which is scarcely elevated 

 above the margin of the area and not incurved ; sinus shallow, 

 rounded and extended quite to the apex of the beak; area high, 

 nearly flat and slightly inclined towards the front, transversely 

 striate; foramen narrow triangular. Surface ornamented by 

 twenty or more simple rounded plications on each side of the 

 mesial sinus and fold, the lateral ones of which do not reach 

 the beak, but run out along the margin of the area. Faint lines 

 and occasional stronger wrinkles of growth mark the shell con- 

 centrically. 



This species is associated with the last, and may be distinguished from 

 that by its less elevated, smoother, and more numerous plications, and more 

 depressed and rounded mesial fold. It is also proportionally more transverse, 

 and has a flatter area as well as less distinct marks of growth. 



This species may be confounded with S. oweni ; but the area inclines 

 forward, instead of being vertical or slightly arcuate as in that species, and 

 the number of plications in a much smaller individual is fully equal or 

 greater than in the full-grown specimens of that species. 



Geological position and locality. In limestone of the age of the Upper 

 Helderberg group : Falls of the Ohio and Charleston landing, Indiana. 



Spikifer arctisegmentus ( n. s.). 



Pal. N.Y. Vol. iv. 



Shell transversely semioval, length less than one -third the 

 breadth ; hinge equalling the greatest width of the shell, and 

 terminating in mucronate points : dorsal valve depressed con- 

 vex, having about eight simple elevated angular plications on 



