Marylaxd Geological Survey 291 



raised ridges. The species is named for Mr. George M. Eoeder, who first 

 collected it, in recognition of his enthusiastic and careful collecting of the 

 fossils about Cumberland. 



Length 3.4 cm., -width 3.5 cm. 



Orhiculoidea jervensis Barrett ' is another Oriskany species of the 

 higher zones. It is readily distinguished by having a broadly suboval or 

 nearly elliptical outline, depressed ventral valve, and fine concentric lines 

 of growth, instead of the widely placed, high, narrow ridges of 0. ampla 

 and 0. roederi. 



Occurrence. — Oeiskant Formation", Eidgely Member. Cash Valley. 



Collection. — George M. Eoeder. 



Orbiculoidea ampla (Hall) 



Plate LlIT, Fig?. ;]-:) 



Discina gravdis emend, ampla Hall, 18.59, Nat. Hist. N. Y., Pal., vol. iii, p. 

 406, pi. xcii, flg. 1, 1861. 



Description.--' Shell suborbicular or very broadly oval. Dorsal valve 

 very conve.x, the convexity equalling about one-third of the width ; apex 

 subcentral. Ventral valve nearly flat: apex somewhat excentrie, very 

 slightly elevated in front of the foramen, and the space between this and 

 the anterior margin slightly concaAe ; foramen oblong, narrow oval, the 

 depression on the exterior of the shell extending from the apex to near 

 the posterior edge. Surface marked by strong elevated concentric lamellose 

 striae, and, on the interior of the shell, by radiating vascular impressions." 

 Hall, 1859. 



Diameter about 5 cm. 



Occurrence. — Oriskany Formation, Eidgely Member. In loose 

 blocks at Miller's Spring, Eidgely, West Virginia; sections along the 

 North Branch in Washington County, Maryland. 



CoUection. — Maryland Geological Sun'ey. 



• See Weller, 1903, Geol. Surv. N. J., Pal., vol. iii, p. .343, pi. xlv, figs. 7, 8. 



