348 NORTH AMERICAN INDEX FOSSILS. 



33. D. typa Ulrlch. (Fig. 1658, s,s', t.) Ordovicic. 



Extremities nearly equally rounded, with a slight flattening of 

 anterior margin. 



Black River of Minnesota. 



XVI. EuRYCHiLiNA Ulrich. 



Oblong or semielliptical shells, having a subcentral primitia: 

 sulcus, the posterior edge of which is often raised into a small 

 rounded node; hinge straight, nearly equalling the length of the 

 shell ; anterior, ventral and posterior margins provided with a wide,, 

 often radiately marked, frill-like border, usually curved on its 

 inner side so as to form a concave area around the true contact 

 edges of the valves. Twenty or more species. Ordovicic. 



(In a section of this or a closely related new genus of which 

 E. obesa Ulrich and Primitia plana Krause are good representa- 

 tives, the valves show neither a well defined sulcus nor a node.) 



34. E. reticulata Ulrich. (Fig. 1657, />.) Ordovicic. 

 Elongate, with broad, radially striated, flat marginal frill ; sulcus 



posterior of center; anterior end long. (Type of genus.) 

 Stones River and Black River of Minnesota, etc. 



35. E. equalis Ulrich. (Fig. 1657, g-.y.) Ordovicic. 

 Shorter than preceding and proportionately higher and more 



symmetrical; sulcus central; margin smooth, thick, rounded. 

 Chazy of Kentucky and Tennessee. 



36. E. striatomarginata (S. A. Miller). (Fig. 1657, ^0 Ordovicic. 

 Differs from preceding in slightly greater elongation and less 



prominent, finely striated marginal rim. 

 Upper Cincinnatian of Indiana. 



XVII. Macronotella Ulrich. 



Shell semicircular or semiovate, with a long, nearly straight 

 hinge; valves equal, inflated centrodorsally, without ridges or 

 sulcus, but exhibiting a smooth subcentral spot where the reticular 

 ornament is omitted. Ordovicic. 



37. M. scofieldi Ulrich. (Fig. 1657, i^^i^.) Ordovicic 

 Hinge line forming greatest width of shell; ends acute or rect- 



I 



