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



ment fits; each pleura is provided with a well-marked groove which 

 originates at the dorsal furrow and extends on to the flattened distal 

 portion of the segment. The pleural segments curve regularly upward 

 for about one-third their length, then abruptly to the lateral margins. 



Pygidium transversely suboval in outline with posterior portion pro- 

 duced into an obtuse angle, strongly trilobed. The convex axis tapers 

 posteriorly and terminates on a rounded extremity near the posterior 

 margin, marked by seven annulations. The pleural lobes slope abruptly 

 from the dorsal furrows to the margins, each lobe consisting of five or 

 more segments, the anterior ones being distinct and the others becoming 

 less so until they are entirely obsolete at the posterior extremity of the 

 pygidium; each segment is marked by a shallow longitudinal groove 

 which originates at the lateral margins and becomes obsolete before 

 the dorsal furrow is reached. 



The dimensions of the type specimen are: Length of cephalon 10.5 

 mm.; width 18.3 mm.; length of thorax 21.5 mm.; length of pygidium 

 3.5 mm.; width 9.3 mm.; entire length of the body 39 mm. measured 

 around an enrolled specimen, but if the test was unrolled it would 

 measure 3 or 4 mm. less. The cephalons of two specimens in the col- 

 lection of Mr. A. G. Becker measure respectively 13.5 mm. long, 24 mm. 

 wide, and 9.5 mm. long, 15.6 mm. wide. All of the specimens on which 

 the description is based are enrolled specimens so that it is difficult to 

 take accurate measurements of some of the parts. 



Remarks. — This species has been referred by most writers and 

 collectors to C. senaria of the Ohio Valley region, but upon comparing 

 practically perfect specimens from the two localities they are found to be 

 distinct. The glabella in C. senaria is shorter and more convex, the 

 pleural segments of the pygidium do not have a longitudinal furrow, 

 the lip-like process on the anterior margin of the glabella is shorter and 

 the surface of the test does not possess the rounded tubercles. C. mam- 

 millata was described from the Maquoketa of Dubuque Co., Iowa, and 

 specimens from the type locality loaned to the Museum for study from 

 the collection of the State University of Iowa by Prof. George F. Kay 

 prove C. fayettensis to be quite dissimilar. The frontal lip is very 

 large in C. mammillata and bears a low, rounded tubercle just in front of 

 each dorsal furrow. The surface ornamentation is also quite different. 

 C. fayettensis resembles C. christyi in the outlines of the glabella, but 

 there the similarity ceases as it does not possess the genal spines or the 

 curvature of the thoracic segments, and the form and size of the pygi- 

 dium are entirely unlike. The surface ornamentation of C. fayettensis 

 is similar to that of C. niagarensis, but in the form of the glabella and 

 many other characters it is entirely distinct. 



