264 THE CHICAGO ACADEMY OF SCIENCES. 



forward to become confluent with the third lateral furrows; 

 occipital segment broadest in the middle, its surface slightly 

 higher than that of the glabella on the median line. Cheeks 

 convex, depressed below the glabella, marked laterally by con- 

 spicuous marginal furrows continuous with the posterior cheek 

 furrows which extend to the dorsal furrows, their terminations 

 being opposite the extremities of the occipital furrows; the con- 

 vex lateral and posterior marginal borders are produced back- 

 ward, where they become confluent, into the slender genal spines; 

 palpebral lobes small, eyes and free cheeks not observed. The 

 surface of the cheeks lying between the bounding furrows is 

 pitted, the pits being more or less rounded in shape and crowded 

 together. 



Pygidium broad and short, the axis wedge-shaped with three 

 annulations and' a narrow, posterior, 'median extension which is 

 produced a little beyond the posterior margin; pleura flat and 

 broad with three segments which are produced laterally in 

 flattened spines directed obliquely outward and backward with 

 a slight curve, the posterior pair of spines are much shorter than 

 the others, and the anterior pleural segments are grooved 

 proximally. 



The dimensions of a nearly perfect cranidium are: width 

 55 mm., length along median line 24.5 mm., length of genal 

 spines about n mm. The dimensions of a nearly perfect pyg- 

 idium are: extreme width 26 rnm., width between the bases of 

 the anterior pleural spines 17 mm., length along median line 

 7 mm. 



Remarks. The geographic distribution of this species is 

 widespread in the Niagaran formations of the Mississippi valley 

 region, although it never seems to be a common species. It is 

 a close ally of the European species C. insignis, and in earlier 

 years w^as frequently so identified. 



Localities. Hawthorn, Chicago Drainage Canal near Le- 

 mont, etc. 



Ceraurus hydei, n. sp., pi. xxiv. fig. 22. 



Description. A small species. Cephalon semi-circular in 

 outline with rather slender genal spines whose extremities are 

 opposite the posterior margins of the third thoracic segment. 

 Glabella moderately convex, broadest in front, bounded by well 

 defined dorsal furrows, its anterior margin not reaching the fron- 

 tal margin of the head, its posterior margin occupying two- 

 sevenths of the entire width of the head; frontal lobe sub- 



