526 PALEONTOLOGY OF ILLINOIS. 



rounded in front and straight behind, with posterior lateral 

 angle terminating in short, pointed, spine-like appendages 

 extending back to the third thoracic segment. Glabella 

 ovate, tumid, contracted and depressed behind, widest and 

 most convex or ventricose anteriorly, where it is about one- 

 third narrower than its length from the neck segment to its 

 rounded front, which is not margined by a projecting rim; 

 very distinct from the cheeks in consequence of its greater 

 convexity ; posterior lateral lobes small, much depressed, and 

 isolated by the oblique lateral furrows in the front being so 

 directed as to intersect the neck furrow; immediately in 

 front of these there are on each side faint traces of another 

 small, very obscurely defined, lateral lobe; anterior lobe 

 ovate, ventricose, and comprising more than nine-tenths 

 of the whole; neck furrow deep and broad; its continua- 

 ation across the posterior side of the cheeks distinct, straight, 

 and terminating at the lateral furrows of the cheeks; neck 

 segment prominent, twice the size of the thoracic segments, 

 and equaling the greatest transverse diameter of the glabella 

 in front, but more depressed. Eyes in the form of* some- 

 what oval, ventricose tubercles, considerably lower than the 

 glabella, from which they are separated by rather wide, dis- 

 tinct depressions, placed about half their length in advance 

 of the posterior margin of the cheeks, and without visible 

 facets ; palpebral lobes depressed, not covering the eyes, but 

 merely connecting with their inner sides, so as to leave the 

 visual area forming an almost isolated tubercle. Cheeks 

 sloping from the eyes into a broad, deep marginal sulcus, 

 which is not continued around the front of the glabella, but 

 extends back a little upon the lateral spine ; outside of this 

 there is a thick, distinctly striated marginal rim, which be- 

 comes very nearly obsolete around the front of the glabella. 

 Facial sutures cutting the anterior margin nearly on a line 

 with the eyes, but curving so as to leave a small semi-cir- 

 cular wing on each anterior lateral margin of the glabella; 

 behind they intersect the posterior margin of the cheeks 



