ORTHIDES OF THE PORTAGE AND CHEMUNG GROUPS. «3 



Orthis thieinei? 



PLATE VIII. 

 Orthis thiemei? White, Journal of the Boston Soc. Nat. History, Vol. vii, p. 231. 



Among the Orthides from Cattaraugus county are some casts, that 

 bear 'a very close resemblance to this species of the arenaceous beds at 

 Burlington, Iowa. The ventral valve is flattened or depressed in the 

 middle below the muscular impression, and the sides are narrowed to- 

 wards the hinge-line, which is shorter than the width of the shell. 



The casts of ventral valves referred to this species occur in the same beds with 

 0. leonensis; and it is not impossible that the dorsal valves like fig. 5, Plate viii, 

 may belong to the same. 



Geological formation and locality. Arenaceous beds of the Chemung group, near 

 Leon, Napoli and New- Albion, Cattaraugus county. 



Orthis leucosia? 



PLATE VIII. 

 Compare Orthii leucotia, Plate vii, p. 48, this volume. 



Figsi 9 and 10 are representations of the exterior of the shell of a 

 dorsal valve, and the cast of a ventral valve, which occur in a specimen 

 of olive shaly sandstone, labelled as from Steuben county. The specimen 

 contains, besides these, the impression of a Pkoductus and of Leiorhtn- 

 CHUS, giving the character and aspect of the Chemung rocks ; but it is 

 the only specimen in which this Orthis has been observed, and it seems 

 to me possible that it may have been derived from some of the higher 

 and more arenaceous beds of the Hamilton group in the eastern part of 

 the State, where the lithological characters of the two formations are 

 very similar. 



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