99 PALAEONTOLOGY OF NEW-YORK. 



Discina tuUia ( n. s.)- 



PLATE II. 



Dorsal valve elliptical ; apex excentric, elevated above the plane of the 

 margins of the shell nearly one-eighth of an inch ; length half an inch, 

 and breadth little more than three-tenths of an inch. 

 ScBFACE marked by fine crowded striae. 



A single specimen of the dorsal valve only has been seen, but its proportions 

 of length and height distinguish it from any other species in the rocks of New- 

 York. 



Geological formation and locality. In the Tully limestone near Ovid, Seneca 

 county, N.Y. 



Disciiia lodensis. 



PLATE II. 



Orbicula lodentu : Hall, Geological Report Fourth District, p. 223. 

 — — : Vanuxim, (xeological Report Third District, p. 168. 



Shell broadly oval-ovate or subcircular, narrower towards the posterior 

 end. Dorsal valve very depressed -convex ; apex minute, excentric, 

 less than one-third the length of the shell from the posterior margin. 

 Ventral valve flat towards the margins, and somewhat abruptly ele- 

 vated at the apex ; foramen linear, extending more than halfway from 

 the apex to the margin, and sometimes causing an undulation of the 

 edge, or slight emargination. 



ScEFACE finely striated concentrically by close crowded and little elevated 

 BtrisB, and, on the anterior half of the shell, by faint radiating folds or 

 undulations. In partially exfoliated specimens, radiating marks of the 

 vascular impressions are perceptible. Specimens rarely show the con- 

 centric striae to be crenulated by delicate radiations, a character which 

 undoubtedly existed in all perfect shells. 



In the partially exfoliated shells, the apex of the dorsal valve shows a 



