522 Contributions to Invertebrate Palaeontology. 



from American rocks, and will not easily be mistaken. It resem- 

 bles, in the features of the dorsal valve, specimens of Ortlvis flabel- 

 lum from the shales of the Niagara group of New York and else- 

 where ; but it is more coarsely marked, with wider and more deeply, 

 concave interspaces. 



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

 derberg group, at Smith and Price's quarries, near Columbus, Ohio. 

 Collected by Mr. Hyatt. 



Genus RHVIVCHONELLA Fischer. 



Rliynclioiiella? raricosta. 



Plate VI, fig. 6. 



Rhynchonella raricosta Wliitf., Aun. N. Y. Acad. Sci., March, 1882, p. 201. 



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 greatest 

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

 Front of the valve broadly curved, and marked by several deep indentations 

 corresponding to the number of plications marking the surface. Middle of the 

 valve marked by a broad, shallow, slightly angular mesial sinus, which is 

 more than one-third 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, by two low, 

 angular, but distinct plications, besides those bordering 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 tliat 

 of the mesial sinus, and probably corresponding 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 ven- 

 tral valve and the small number of low, angular plications, will 

 readily distinguish this from any species 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 Helderberg 

 group, at Smith and Price's quarries, near Columbus, Ohio. Col- 

 lected by the Hyatt brothers, of the State University. 



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