AV/r Spvcics (if Fn.ssil-'< from (Jliiu. 201 



indicates its true position. It is entirely unlike any species 

 hitherto described from American rocks, and will not easily l)e 

 mistaken. It resembles, in the features of the dorsal valve, 

 specimens of Ortliis flahefbtni from the shales of the Niagara 

 grouj) of NcAv York and elsewhere ; but it is more coarsely 

 marked, with wider and more deeply concave interspaces. 



Formation and Local ily. — In the limestones of the Upper 

 Ilelderberg group, at Smith and Price's quarries, near Columbus, 

 Ohio. Collected l)y Mr. Hyatt. 



Rliynclioiiella^ raricosta, n. .sp. 

 Pal. O., Vol. Ill, Plate 2, Fig. (5. 



Shell of moderate size, and somewhat transversely sub-triangular in out- 

 line, when seen upon the ventral side. Ventral valve flattened and very 

 shallow, with a short, obtuse, and not at all incurved beak ; cardinal slopes 

 incurved, and the margins straight from the beak to near. the point of great 

 est width of the valve, the angle of divergence being nearly or quite 120 

 degrees. Front of the A-alve broadly curved, and marked by several deep 

 indentations corresponding to the number of plieations marking the surface. 

 Middle of the valve marked by a broad, shallow, slightly angular mesial 

 sinus, which is more than one-thiixl as wide at the front of the valve as the 

 length from beak to base. Surface of the valve marked, on each side of 

 the sinus, bj^ two low, angular, but distinct plications, besides those bor- 

 dering the sinus ; no other markings are traceable on the surface of the 

 shell. The margin of the valve between the plications is extended, forming 

 rounded projections similar to that of the mesial sinus, and probably cor- 

 responding to low rounded plications which have characterized the dorsal 

 valve, which has not been observed. 



The broad sub-triangular form of the shell, with the shallow 

 ventral valve and the small number of low, angular plications, 

 ■will readily distinguish this from any si)ecies hitherto known. 

 There may possibly be some doubt as to the generic reference 

 of the species : but this cannot be positively determined until 

 more perfect individuals are obtained. 



Formation and Locality. — In limestone of the Upper Helder- 

 berg group, at Smith ;ind Price's quarries, near Columbus, Ohio. 

 Collected by the Hyatt 1)ruthers. of the State University. 



L AME LLI BR ANC HI AT A. 



GeiiUiii Mjlilarca, H. and W. 



Frdhn. Xotice LumeUibr<iric]iiat(' Shells, Up. IIi'Ul , llani.itud i'Ih^iuhjuj (rraaps. d'c 

 Stale Cab. Nat. Hist., Dee.. ISOD. 



