Length of the head, in the best preserved specimen, in a straight line, 

 is 4 lines ; length, following the curve of the surface, 7 lines ; width at 

 the posterior margin 13 lines ; between the points of the spines 15 lines ; 

 width of glabella 2 J lines ; distance of the eve from the neck furrow 2J 

 lines ; distance of the centre of the eye from the posterior margin 1 J 

 lines ; length of the eye a little more than half a line. The spines extend 

 about 6 lines backwards from a line drawn across the head at the pos- 

 terior margin. 



This extraordinary trilobite is clearly allied to I. Bayfieldi and /. 

 consobrinus, more particularly to the latter. There are some specimens of 

 the latter with the head shorter and broader than the one figured, and 

 approaching this species in form. Still the extreme arcuation of the 

 head, and the contraction of the cheeks into cylindrical spines, distin- 

 guishes this sufficiently to authorise a separate name. 



Locality and Formation. P, Cow Head, Newfoundland ; Quebec 

 group. 



Collector. J. Richardson. 



CONSOBRINUS. (N. sp.) 

 b 



Fig. 266. 

 Fig. 266. lllanus consobrinus. a, the upper side of the head, 6, side view of the same. 



Description. Head short, proportionally very wide, strongly arched 

 from the posterior to the anterior margin, most elevated point at one-third 

 the length, from behind ; anterior margin gently convex in the middle half 

 and more abruptly towards the angles ; the latter well rounded. The 

 middle lobe or glabella is about one-third the whole width in a straight 

 line from angle to angle, gently convex, and extends one third the whole 

 length (measured along the curve of the surface) ; dorsal furrows well 

 defined, the eyes are rather small, lunate, depressed convex on the 

 outside, level with the surface on the inside, distant from the dorsal furrows 

 half the width of the glabella, a little less than their own length from the 

 dorsal margin, and the width of the glabella from the posterior angles to the 

 head. Surface with the usual concentric striae. 



The best preserved specimen measures in a straight line between the 

 posterior angles, 9J lines. Length of the head measured on the curve 8| 



