432 Systematic Paleontology 



Length 8 mm. ; width 10 mm. 



Occurrence. — Helderberg Formation, Kbyser Member. Devil's 

 Backbone, Cash Valley. New Scotland Member. Cumberland, Mary- 

 land ; Cherry Run, West Virginia. Becraft Member. Cherry Eun, West 

 Virginia. Oriskany Formation, Ridgely Member. Cumberland. 



CoZ/edion.^Maryland Geological Survey. 



NUCLEOSPIRA SWARTZI n. sp. 



Plate LXXIII, Figs. 15-17 



Description. — Shell subcircular to transversely subelliptical in outline, 

 subglobose. Breadth greater than length. Cardinal, lateral, and anterior 

 margins rounded. Hinge-line shorter than the greatest width of the shell. 

 Ventral valve convex, gibbous, greatest convexity about one-third the 

 distance from the bealc to the front ; beak pointed and prominent, strongly 

 incurved over that of the dorsal valve. In some individuals there is a faint 

 undefined shallow sinus which may extend from the beak to the front, 

 producing at the front a slightly emarginate appearance. Dorsal valve con- 

 vex, less so than the ventral valve, approaching to depressed convex, point 

 of greatest convexity about one-third the distance from the beak to the 

 front; beak prominent and incurved under that of the ventral valve. 

 Sometimes an indistinct mesial depression marks the anterior portion of 

 this valve. Surface of both valves marked by indistinct concentric lines 

 of growth which become more prominent towards the front where they 

 become distinct concentric lamellae. 



This species is closely related to N. elegans from which it differs in 

 being less transverse, its outline being more nearly subquadrate. It also 

 differs in the lesser convexity and much less distinct sinus of brachial valve. 



Dimensions : Large individuals 18 mm. wide, 16 mm. long. 



It differs from N. ventricosa in being less globose, larger, the ventral 

 valve much more convex than the brachial valve. The valves are of almost 

 equal convexity in Nucleospira ventricosa. 



Length 1.5 cm. ; width 1.6 cm. 



Occurrence. — Helderberg Formation, Keyser Member. Cookerly, 

 Devil's Backbone, Cash Valley, Maryland; Keyser, West Virginia. 



Collection. — Maryland Geological Survey. [Maynard.] 



