72 Field Museum of Natural History — Geology, Vol. IV. 



sutures originate on the lateral margins about in line with the occipital 

 furrow, curve forward and inward to the palpebral lobes, which they 

 traverse, thence pass forward with a sigmoid curve to the anterior mar- 

 gin of the cephalon. 



Thorax composed of ten segments; axis convex, about the same 

 width as the pleurae; pleurae flattened for one-third to onerhalf their 

 width from the dorsal furrows, then bent downward and backward, 

 tapering to a point; each pleural segment is ornamented with a promi- 

 nent tubercle situated near the point where the pleurae curve downward; 

 an angular furrow originates on the anterior margin of each pleural seg- 

 ment at the dorsal furrow and crosses it obliquely, reaching the posterior 

 margin behind the tubercle; dorsal furrows distinct, nearly parallel 

 from the first to the eighth thoracic segment, then converging poste- 

 riorly. 



Pygidium short, much narrower than the posterior segment of the 

 thorax, consisting of three segments; the anterior segment bears a pair 

 of stout spines, which extend posteriorly with the points somewhat con- 

 verging; axis undefined. 



Surface of the cephalon, within the marginal borders, covered with 

 irregularly placed tubercles; on the cheeks the tubercles are somewhat 

 farther apart and the interspaces are pitted; the marginal borders and 

 genal spines are finely granulose; two or more conical tubercles are 

 situated on the posterior borders of the cheeks; the entire thorax is 

 finely granulose, as is also the pygidium, but the granulations are more 

 conspicuous on the caudal spines. 



Measurements of the type are as follows: 



Length on median line 28.7 mm. 



Length including caudal spines 35.4 mm. 



Width at genal angles ; 21.6 mm. 



Width at points of genal spines 23 . 6 mm. 



Length of cephalon including genal spines 11. 5 mm. 



Length of glabella 8.0 mm. 



Width of posterior lobes of glabella 6.0 mm. 



Width of anterior lobe of glabella 7.5 mm. 



Width of pygidium 7.4 mm. 



Length of pygidium 2.7 mm. 



The above description is based on the type specimen from Cincin- 

 nati, Ohio, No. 6062 of the paleontological collection of the University 

 of Chicago. The species is known to the writer from Fayette County by 

 twelve more or less complete cephalons and two pygidia. These agree 

 with the type except that in the type the genal spines are somewhat 

 shorter, the tubercles on the posterior border are less conspicuous and 



