FOSSILS OF THE COAL MEASURES. 565 



sutures between the plates. Surface of body and arms ap- 

 parently smooth. 



Hight of body to top of first radials, about 0.18 inch; 

 breadth of do., 0.65 inch; hight to top of ventral portion, 

 including the body, 1/20 inches; breadth of the flattened 

 top of the ventral portion, exclusive of the free marginal 

 spines, about 0.50 inch. 



The form of the body and the arrangement of tbe anal pieces of this 

 species are very similar to those of our Z. tf/.scw, from the upper Coal 

 Measures, but its under side is more decidedly concave, its first radial 

 pieces proportionally higher, and separated by decidedly deeper sutures. 

 Its subradials are also proportionally smaller. From Z. mitcroxphtus, of 

 McCiiESSEY, it is at once distinguished by not having its second radial 

 pieces developed into spines, and by the different structure of its arms. 



The specimen here figured was found and presented to one of the 

 authors by Mr. DAVID WILLIAMS, of Canton, Illinois. 



Locality and ptmition Sea ville, Fulton county, Illinois ; roof of Coal 

 No. 1. 



Genus EUPACHYCKIXT s. 

 EUPACHYCKINUS FAYETTEXSIS, TTorthen Ms. 



PL 24 : Fig. 10. 



BODY below the top of the first radials basin-shaped, 

 base rather deeply impressed, more than twice as wide as 

 high, and composed of massive, slightly convex plates. 

 Subradials considerably higher than wide, four pentago- 

 nal and one hexagonal, their upper angles extending up 

 above the middle of the first radials, the one on the 

 anal side giving support to a small anal piece. First ra- 

 dials larger than the subradials, nearly twice as wide as 

 high, and truncated straight across their upper margins, 

 where they give support to the second radials, with a some- 

 what gaping suture between. Second radials as wide as 

 the tirst, and produced on their outer sides into short, 

 rather obtuse spines. One anal piece only is seen im- 

 planted directly bet wren the first radials. and supported 



