294 NORTH AMERICAN INDEX FOSSILS. 



aa. Surface of head marked with wave-like wrinkles. 



99. 7. americanus. 



aa. Surface of head marked with coarse lines 100. L crassicnuda. 



a. Head without upward bending of the anterior margin 22. 



22. Dorsal furrows of head deeply impressed bb. 



bb. Sides of the pygidium truncated almost at right angles to anterior 



margin 98. 1. latiaxiatus. 



bb. Sides of pygidium not abruptly truncated 96. I. globosus. 



22 Dorsal furrows of head not deeply impressed loi. /. ioxus. 



95. I. consimilis Billings. (Fig. 1604, a.) Ordovicic. 

 Differs from /. americanus in the nearly flat glabella. Entire 



surface covered with rudely concentric, fissure-like striae. Free 

 cheeks produced very far laterally, giving to the head a very broad 

 appearance ; the posterior margin of the free cheek outside the eye 

 forms an angle of 50° with the lateral margin of the cheek; in 

 f. americanus the angle is 90° to 100°. 

 Quebec group, Div. L, M, N (Chazy), of Newfoundland. 



96. I. globosus Billings. (Fig. 1605, a, c) Ordovicic. 



b ^ 



Fig. 1605. a, c, Illienus globosus, dorsal and side views; b, Thaleops ardura, nat. 

 size. (After Raymond.) 



The short dorsal furrows deeply impressed. Genal angles 

 rounded. Thorax of ten segments ; axis very wide ; dorsal furrows 

 deep. Pygidium unsegmented. 



Chazy of New York, Montreal, and Mingen Islands. 

 97. I. angusticollis Billings. Ordovicic. 



Cephalon with deep dorsal furrows, only posteriorly impressed. 

 Eyes large. Free cheeks extended into sharp spines. Thorax 

 with narrow axis and deep dorsal furrows. Pygidium short and 

 wide with axis extending about half its length. Entire test finely 

 [)unctate. 



Black River of Ontario and Quebec. 



