277 



idlum, the fold of the crust below extends about half the length, and in the 

 cast of the inner surface there is a rounded groove extending from near the 

 apex of the axis backwards becoming obsolete before reaching the margin. 



Surface of the head and pygidium with numerous flexuous fissure-like 

 strije, three or four in one hue, having a rudely concentric arrangement 

 sub-parallel with the margin. 



This species is certainly most closely allied to /. crassicauda both in form 

 and surface markings. It seems however to be a smaller species, for though 

 the specimens are numerous, none that I have seen could have been, when 

 perfect more than one and a half inches in length. /. crassicauda has the 

 posterior part of the pygidium very tumid, and a sharp elevated rim border- 

 ing the anterior margin of the head, characters which are not possessed 

 by I. f rater mis. 



Locality and Formation. — L, Point Rich ; and N, Table Head ; P, 

 four miles N. E. from Portland Creek, Newfoundland; Quebec group. 



Collector. — J. Richardson. 



Ill^nus consimilis. (N. sp.) 



Fig. 263. a, 6, c. 



Description. — This is a large species, and closely allied to I. Aviericanus 

 of the Trenton limestone. The length of the head (measured along the 

 surface following the curve) is about two-thirds the whole width ; glabella 

 defined by the dorsal furrows for about one-third the whole length, and its 

 width equal to about half the whole length. The anterior two-thirds of 

 the head form a broad, moderately and uniformly convex front, inclined 

 at an angle of from 80° to 90° to the plane of the posterior third. The 

 glabella is very gently convex, and the space between it and the facial 

 suture on each side is nearly flat. The anterior margin is gently convex 

 nearly all round the front, a little concave just outside of the facial suture, 

 and has a small, sharp, elevated rim on the edge, which becomes obsolete 

 just before reaching the posterior angles, the latter narrowly rounded. 

 Eyes apparently depressed, lunate, distant from the dorsal furrows about 

 half the width of the glabella, and half their own length from the posterior 

 margin. They appear to be about 2^ lines in length in individuals of full 

 size. 



Thorax with ten segments ; axis a little more than one-third the whole 

 width, and tapering a little backwards ; side lobes flat on each side for a 

 little more than half their width ; pleural angle well defined, about 45^. 



Pygidium semi-elliptical, greatest width equal to about twice the length; 



