402 PALEONTOLOGY OF ILLINOIS. 



the one on the anal side, which is larger than the others, and 

 heptagonal in outline. First radial pieces rather smaller 

 than the largest subradials, somewhat wider than high, 

 with a general subpeiitagonal form ; all strongly incurved 

 above between the free radials ; facet for the reception of 

 the second radials about one-third the breadth of the first 

 radials, and rather deeply excavated. Anal piece rather 

 smaller than the first radials, longer than wide, irregularly 

 hexagonal, and supporting the outer side of the ventral 

 tube (proboscis), which, like the body, is composed of very 

 thin plates. Second (first free) radials very small, short, 

 and not always extending entirely across the excavation 

 for their reception; succeeding radials, excepting the last, 

 quadrangular, as viewed on the outside, about twice as 

 wide as long, and abruptly rounded or subangular on the 

 outside; last one pentagonal, and generally a little longer 

 than the others. Of these free radials four may be counted 

 in one of the posterior rays, six in the other, three in one 

 of the lateral rays, and seven in the anterior ray. 



Arms at their origin on the last radials rather divergent, 

 and in one of the posterior rays seen to bifurcate on the 

 sixth piece, above which one of the divisions can be traced 

 to the sixth piece without further bifurcation, though there 

 are probably other divisions beyond; arm pieces about as 

 long as wide, and, like those of the free radials, all deeper 

 than wide, and profoundly grooved within for the recep- 

 tion of the ambulacra! organs. Surface smooth or only 

 very finely granular. 



Hight of body, 0.50 inch.; greatest breadth of same, 

 about 0.75 inch. 



This species is related to C. rotnndatus, Hall, but not only differs in 

 having its free radial series much stouter (judging from the facets for 

 their reception in the typical specimens of that species now before us), 

 but in having all of its body plates very decidedly thinner, while its 

 first radials also differ in curving strongly inward, between the bases 

 of the free rays. It likewise comes from the lower division of the Bur- 



