FOSSILS OF THE NIAGARA GROUP. 



419 



are more prominent. The more conspicuous difference, however, is the 

 prolongation of the posterior angle of the cheek into a short strong spine, 

 a feature which 1 have not observed in /. barriensis. The pygidium is 

 also more nearly semicircular, being broader in proportion to its length. 

 Formation and Locality. — In limestone of the Niagara group at Bridge- 

 port, Illinois, and at Grafton and Racine, Wisconsin. 



Ill^nus insignis, n. s. 



PLATE XXII, FIGS. 13, 14. 



Head large ; glabella prominent and somewhat regularly arcuate from 

 front to base ; anterior border with the margin a little recurved. 

 Dorsal furrows distinctly marked from the base of the head for 

 three-fourths the distance to the anterior margin, where they ter- 

 minate in a distinct rounded pit; palpebral lobe large, elongate, the 

 eye being situated at some little distance from the posterior margin 

 of the head. Facial suture running out on the anterior border 

 within the line of the eye. The full extent of the cheek is not 

 known. The form of the glabella and the convexity of a single 

 articulation of the thorax indicate the general form to have been 

 very convex. 



The pygidium is parabolic, very convex; about as long as wide or 

 a little longer. Anterior margin nearly straight along the middle for 

 about half the width, for the attachment of the axis of the thorax, and 

 abruptly receding towards the sides. 



Fig. 10. 



Fig. 11. 



The specimens are mostly casts of the interior, but the species is 

 readily recognized by the elongate and regularly arcuate form of the 

 glabella, and the strongly marked dorsal furrows, and in these respects 

 it differs conspicuously from any other species in the formation. A 



