298 NORTH AMERICAN INDEX FOSSILS. 



107. B. trentonensis Emmons. (Fig. 1610, a, &.) Ordovicic. 



Very convex. Cephalon with no prominences except the eyes. 



Fig. 1 610. a, b, Bumasius trentonensis, enrolled and extended ; <r, d, Nileusvigi/ans, 

 two views of enrolled individual. (After Clarke.) 



Trenton of New York, New Jersey, Illinois, Wisconsin Minne- 

 sota and Quebec. 



108. B. niagarensis Whitfield. {Illcenus madisonianus Whitfield.) 



Siluric. 



Cephalon differs from that of /. insigms in its subelliptical out- 

 line, less convexity, and absence of lip-like border ; pygidium differs 

 in the absence of the median ridge and in the presence, posteriorly, 

 of an ill-defined concave border. Thorax of 10 segments and with 

 no indication of dorsal furrows. 



Clinton of Ohio ; Niagaran of Illinois, Wisconsin and Arkansas. 



XLIV. Thaleops Conrad. 



Very similar to Illcenus but with deep lobation of cephalon pos- 

 teriorly, long, attenuate, projecting free cheeks, eyes borne on de- 

 pressed, divergent stalks. Genal spines blunt, short and project- 

 ing. Axis of pygidium deeply defined. Entire surface punctate. 

 Ordovicic. 



109. T. arctura (Hall). (Fig. 1605, ^.) Ordovicic. 

 Differs from T. ovata in its more prominent palpebral lobes 



which rise at an angle of about 30° with the surface of the fixed 

 cheeks. Genal spines smaller and with nearly circular cross 

 section. 



Chazy of Vermont and New York; Black River of Ontario. 



no. T. ovata Conrad. Ordovicic. 



Genal spines strong, with a keel on the upper surface, thus giv- 

 ing a triangular cross section. Palpebral lobes at same level as 

 summit of fixed cheeks. (Type of genus.) 



