292 Systematic Paleontology 



Orbiculoidea schucherti n. sp. 

 Plate LIII, Figs. 6, 7 



Description. — Shell subcircular, concavo-convex. Dorsal valve convex, 

 apex slightly excentric, posterior slope slightly concave. Ventral valve 

 nearly flat, its surface undulating a little. Foramen large, its anterior 

 end a little back of center of valve. Surface ornamented by concentric 

 lamellae and intermediate iiner striae. 



Diameter 10 to 15 mm. 



Occurrence. — Helderberg Formation, Keysek Member. Dawson. 



Collection. — Maryland Geological Survey. 



[Swartz.] 



Orbiculoidea sp. 



Description. — Fragments of a species of Orbiculoidea have been found 

 in the New Scotland member which appear distinct from the other de- 

 scribed species. They are too poor to permit specific determination. 



Occurrence. — Helderberg Formation, New Scotland Member. 

 Devil's Backbone. 



Collection. — Maryland Geological Survey. 



[Swartz.J 



Family TREMATIDAE 



Genus SCHIZOCRANIA Hall and Whitfield 



Schizocr^vnia sp. 



Description. — A single much crushed dorsal valve of a large species of 

 Schizocrania has been found in the New Scotland. Its length is about 

 25 mm. and the width about 20 mm. It is marked by fine radial striae 

 of which there are thirteen in 5 mm. near the anterior margin, and these 

 are crossed by exceedingly delicate concentric lines, causing them to be 

 very finely nodose on the upper edge. There are also concentric rugosities. 



The species seems to be nearest to ^S". superincreta Barrett, but it has a 

 finer and more strongly nodose ornamentation. The latter is from the 



