53 Helderberg FoRMATioisr IN Maryland 



extend to the margin of the pygidium and are separated by broad, concave 

 furrows. The dimensions of the type specimen are : Length 33 mm. ; 

 width 40 mm. ; convexity 9 mm." Weller, 1903. 



The individuals in Maryland are smaller than those from New Jersey. 

 However, the characteristics, i. e., the absence of any spinous extension 

 from the posterior extremity, the absence of any flattened or concave 

 marginal border and the sharp pleural angular ribs which are present, 

 distinguish this species conspicuously from other members of the genus. 



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

 Backbone, Cash Valley. 



Collection. — U. S. National Museum. 



