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



front of the glabella; marginal borders prominent, defined by shallow 

 furrows; the posterior furrows curve into the lateral furrows just within 

 the genal angles; free cheeks small, less than one-third the size of the 

 fixed cheeks. The surface of the glabella, with the exception of the 

 occipital segment and the cheeks, is covered with more or less regularly 

 distributed rounded tubercles; a larger, more conical tubercle is situated 

 on each fixed cheek, just in front of the posterior furrow, at about one- 

 third the distance from the dorsal furrow to the genal angle. A row of 

 spine-like tubercles traverses the posterior marginal borders of the 

 cheeks, and similar tubercles are distributed over the flattened portions 

 of the genal spines, gradually diminishing in size posteriorly until they 

 become obsolete. 



Thorax not known. 



Pygidium transversely sub-elliptical in outline, aside from the spines 

 length less than half the width; composed of three segments, the ex- 

 tremities of the anterior segment produced into long, stout, flattened 

 spines, which curve outward and backward; second and third segments 

 much smaller; axis not well defined. The surface of the caudal spines 

 is covered with sharp conical tubercles similar to those on the genal 

 spines. The pygidium above described (PL XVII, fig. 5) was not 

 associated with the cephalons but came- from the same horizon at 

 Bloomfield. Its size and the form and ornamentation of the spines are 

 such as might accompany these cephalons and no other cephalons have 

 been observed to which this pygidium could well be referred. 



Measurements 



Length of cephalon on median line 



Width of cephalon at genal angles 



Width of cephalon including genal spines (estimated) , 



Length of glabella 



Width of anterior lobe of glabella 



Width of posterior lobes of glabella 



P 17030 



Width of pygidium 



Length of pygidium 



Length of caudal spines (estimated) 



10.7 mm. 



5-5 " 

 20.0 " 



C. elginensis differs from all other species known to the writer in 

 having extremely long genal spines with spinel-ike tubercles on their 

 flattened portion. It is also distinguished from C. milleranus and C. 

 pleurexanthemus by having the eyes farther apart. It is most nearly 

 related to C. dentatus Raymond and Barton, but the ocular ridges are 

 not present in that species and the eyes are not so far forward. 



Locality and horizon. — The species is known to the writer from 



