No. 109.] 65 



ResemWes Spirifer keteroclitus of Von Buch, but has more plications 

 and a wider foramen, whicli appears to be never quite closed as in that 

 species. The area is also generally less extremely elevated in our shell. 



Geological position and locality. Oriskany sandstone, Cumberland, Md. 



Rhynchonella semiplicata (n. s.). 



Pal. N.Y. Vol. iii, pi. 29, f. 1. 



Shell (in the young state) compressed-ovate, becoming more 

 gibbous and subtriangular : valves nearly equal ; ventral valve 

 slightly more gibbous, most prominent in the middle, and having 

 towards the front a more or less defined mesial sinus, in 'which, 

 there are from one to two plications, while from one to three 

 lateral plications occupy the space on each side of the sinus ; 

 beak closely incurved over that of the opposite valve : dorsal 

 valve depressed-convex, having from two to four rounded pli- 

 cations on each side of the medial fold, whicli is itself bifid or 

 trifid; plications strongly marked in front, and usually becoming 

 obsolete near the middle of the valve. Surface having traces of 

 extremely fine radiating striae, crossed by concentric undulations 

 of growth. 



Geological position and locality. Pentamerus limestone of the Lowe 

 Helderberg group, Albany and Schoharie counties. 



HhTNCHONELLA 8£UiPI.rCXTi.. 



[Senate No. 109.] 



