300 Systematic Paleontology 



Description. — " Shell circularly subquadrate, wider than high. Dorsal 

 valve convex in the middle, and depressed almost equally towards the 

 margins : beak rising but slightly above the hinge-line, with a central 

 depression which is lost before reaching the middle of the valve. Ventral 

 valve very convex near the beak, flattened or depressed towards the base : 

 beak veiy prominent, projecting much beyond the opposite valve, pointed 

 and slightly incurved. Hinge-line less than the width of the shell. Area 

 large, extending nearly two-thirds the entire width of the shell : foramen 

 large and high. Surface finely striated, with frequent bifurcations; the 

 strise curving upwards to the hinge margin." Hall, 1859. 



Length 2.2 cm. ; width 2.5 cm. to 3.0 cm. 



This species, never common in Maryland, is readily distinguished from 

 the associated orthoids by the long and high ventral cardinal area and the 

 regularly convex valves, both of which are equally deep. The interior 

 structure is that of Dalmanella. Mr. Roeder has a ventral valve that is 

 41 mm. long and 46 mm. wide, therefore larger than New York in- 

 dividuals. 



Occurrence. — Helderberg Formation, New Scotland Member. 

 Corriganville, near Cumberland, 21st Bridge, Maryland; near Cherry 

 Run, West Virginia. 



Collections. — Maryland Geological Survey, U. S. National Museum. 



Dalmanella clarki n. sp. 

 Plate LIV, Figs. 7-10 



Description. — Subcircular to transversely subelliptical in outline, wider 

 than long, hinge-line shorter than the greatest width of the shell. Pedicle 

 valve very convex, very gibbous to ventricose, beak pointed and strongly 

 incurved and arched over the cardinal area. Brachial valve depressed 

 convex with a well-defined mesial sinus, which extends from the beak to 

 the front, narrow at the beak and becoming gradually wider towards the 

 front; beak small, pointed, incurved, extending only slightly above the 

 hinge-line. The surface of both valves marked by fine radiating striao, 

 which are prominent and well defined. They increase toward the margin 

 by implantation. The stria; may be alternately coarse and fine, or there 



