428 PALAEONTOLOGY OF ILLINOIS. 



ous angle, a row of little pointed isolated protuberances, presenting a 

 crenate appearance as seen in outline. 



Locality and position Upper division of the Burlington group, Bur- 

 lington, Iowa. Lower Carboniferous. No. 321 of Mr. WACHSMTJTH'S 

 collection. 



ZEACRINUS SERRATUS, M. and "W. 



PI. 1, Fig. 6. 

 Zeacrinus serratus, MEEK and WOKTHEN. Proceed. Acad. Nat. Sci., Phila., 1869, p. 151. 



BODY small, much depressed, or about three times as 

 wide as high, broadly truncated and concave below. Base 

 very small, and nearly or quite concealed by the column 

 in the concavity of the under side. Subradials a little 

 tumid, curving abruptly into the concavity of the under 

 side, and extending about half way up the lateral walls of 

 the body ; three or four pentagonal and one or two on the 

 anal side hexagonal (not counting a very obtuse angle 

 doubtless existing at the middle of the under side of 

 each.) First radials somewhat larger than the subradials, 

 nearly twice as wide as high, and all pentagonal in form, 

 with the upper side equaling the entire breadth. Second 

 radials as wide at the base as the first, and nearly twice as 

 long, each pentagonal in form, and supporting two arms, 

 excepting that of the anterior ray, which is quadrangular, 

 and supports but a single arm; each with a prominent, well 

 defined, sharp carina extending up the middle, and the 

 dorsal surface on each side of this carina is distinctly con- 

 cave. Anal pieces arranged in a double alternating series 

 almost exactly as in the last. 



Arms (excepting in the anterior ray) bifurcating first on 

 the sixth piece above their origin on the second radials, the 

 ijmer division being slightly smaller than the other, and 

 simple to the end, while the outer division bifurcates again 

 on the seventh piece above, and a third time on the eighth 

 piece above the latter, the inner divisions being all simple. 

 Arm pieces very short, or two or three times as wide as 



