WAVEELY GEOUP SPECIES. 27V 



» 

 beak narrow, and apparently rather acutely pointed in well preserved 

 specimens; surface ornamented by distinct concentric lines and furrows. 

 Length, 1.06 inch ; breadth, 0.80 inch. 



As I have seen but one mere cast of this shell, I have no means of 

 knowing how far it may vary in form and surface markings, nor of de- 

 termining whether it is a dorsal or ventral valve, though it is more 

 probably the latter. Although it rather closely resembles Mr. David- 

 son's species, I am far from being entirely satisfied that it is really the 

 same. It is proportionally narrower than his figure, and has the concen- 

 tric markings more crowded. The former difference, however, is not 

 greater than often occurs among individuals of the same species, while 

 the latter, as represented in our figure, is a little exaggerated.* It is 

 probably a distinct species, but, without better means of comparison, I 

 do not feel quite willing to separate it. It is even less like the Nebraska 

 Coal Measure form that I have regarded provisionally as a variety of L. 

 Scotica, and can hardly belong to the same species as the latter. 



Lociditu and position : Berea grit, Berea, Ohio. 



Genus DISCIJ^A, Lamarck, 1819. 



(Hist. Nat., yi., 236.) 



Sub genus OUBICLTLOIDEA, D'Orbigny, 1847. 



(Compt. Rend., XX., 269.) 



DisciXA (Orbiculoidea) Newbeeeyi, Hall. 



Plate 14, figs, la, 6, c, d. 



Discina Newberryi, Hall (1864) ; 16th Report of the Regents on the State Cab. Nat. 

 Hist. N. Y., p. 30; and (1867) Paheont. N. Y., IV., 25, pi. 1, figs. 10 and 11. 



Shell rather under medium size, circular, or sometimes very slightly 

 oval, the antero-posterior diameter being in the latter cases a little 

 greater than the transverse. Upper valve much depressed, with its apex 

 placed about half way between the middle and the posterior margin, or 

 slightly nearer the latter than the former. Under valve flat, with point 

 of accretion central, and foramen very small, and situated near the 

 margin at the outer end of a deep oval impression extending from the 

 center nearly to the posterior edge. Surface of both valves marked by 



* The concentric markings are also too strong on our figure, particularly near the 

 beak, where they make a broad curve. 



