329 



Illjsnus Ameeicanus (Billings). 



IlL/Exds Ameiuoanus (Billings). Can. Nat. and Geo., vol. iv, p. 371, October, 1859. 



Fig. 316. 



Fig. 316. — lllanus Americanus. a, upper side of tlie head of the original specimen; 6, 

 front view of the same; f, pygidium of the same; d, a specimen in the 

 cabinet of Dr. J. A. Grant, of Ottawa. 



Desci-iption. — Oblong, distinctly tri-lobed ; length two or three inches ; 

 width from three-fifths to five-sixths the length. 



Head large, strongly convex, its height usually a little greater than its 

 length measured on a straight line, sometimes abruptly bent down at less 

 than half the length from behind, often uniformly arched from the front to 

 the posterior margin, equal to about one fourth of a sphere ; length from 

 front to posterior margin about two-thirds the width between the cheek 

 angles in a straight line. The glabella is moderately convex ; the dorsal 

 furrows extend from one-fourth to a little more than one-third the whole 

 length of the head, measured on^ the curve, and have an obscure sigmoid 

 curve, at first outwards and then inwards, their anterior extremities 

 usually turning a little outwards ; they are distant from each other not 

 quite one-half the whole width of the head. The eyes are of moderate 

 size, about two lines in length, about half their length from the posterior 

 margin, and half the width of the glabella from the dorsal furrows. 



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