278 



angles truncated for one-fourth the length, at an angle of about 80 ; all 

 the rest of the margin broadly rounded ; axis obscurely defined, about one- 

 third of the length ; more distinct in the cast of the interior, where it is 

 conical and narrowly rounded at the apex with an obscure ridge proceed- 

 ing from it to the posterior margin. 



Surface with concentric fissure-like, rudely concentric striae. The 

 pygidium is sometimes nearly smooth. Width of the largest pygidium 

 seen 2 inches ; length 1 inch. 



I have not seen a perfect head of this species, but several deprived of 

 the cheeks. One specimen only, retains the thorax and the pygidium in 

 connection, but without the head. A perfect cheek was found detached, 

 but in the same piece of stone, with several pygidia and portions of the 

 head. 



As before stated, this species is most closely allied to /. Americanus. 

 The only differences that I can see, are the following : In this species the 

 middle lobe of the head is nearly flat, and the surface marked with coarse 

 concentric striae. In I. Americanus the middle lobe is more convex, and 

 the surface covered with short, wave-like wrinkles, not striae. This latter 

 species, however, is an exceedingly rare form, and a larger collection 

 might furnish some with intermediate characters. 



Locality and Formation. L, Point Rich, M and N, Table Head, 

 Newfoundland ; Quebec group. 



Collector. J. Richardson. 



ILLJENUS TUMIDIFKONS. (N. sp.) 



Fig. 264. Fig. 265. 



Fig. 264. Ilkenus tumidifrons. a, the head and pygidium ; b, a rolled up specimen, 



enlarged four diameters. 

 Fig. 265. /. arcuatus. Upper and side views of the head. 



Description. Head exceedingly convex, equal to nearly half of a 

 sphere ; the front part very convex and projecting over the margin ; the 

 posterior angles rounded ; middle lobe well defined, convex, extending 

 one-third the whole length ; eyes moderate, lunate, close to the dorsal 



