302 PALEONTOLOGY OF ILLINOIS. 



Position and locality : The specimen originally described was 

 obtained from the Burlington limestone, near Hamburg, in Calhoun 

 county, and the one figured from the same horizon at Montezuma, 

 in Pike county, Illinois. 



The latter is number 2,471 of the Illinois State collection. 



GENUS ZEACKINUS, Troost. 

 ZEACRINUS COXANUS, Worthen. 



PI. XXVIII. Fie I. 



Zeacrinus (Joxanus, WOBTHEN. February, 1882. 

 Bulletin No. 1, of the Illinois State Museum of Natural History, p. 27. 



Body of medium size, basin-shaped, more than twice as wide as 

 high to the top of the radial series. Base depressed, and the basals, 

 which are small, are concealed by the first columnar joints. Sub- 

 radials hexagonal, once and a half as wide as their height above the 

 basal concavity, which is in part formed by the upward curvature of 

 their lower angles, their upper angles extending up nearly one-half 

 the length of the radial series. 



Eadials nearly twice as wide as long, pentagonal, and truncated 

 squarely across their upper margins for the support of the brachial 

 series. The anterior ray has two brachials, the first one quadran- 

 gular, once and a half as wide as long, and the second short, pent- 

 angular, and supporting the first divisions of the ray. Each division 

 of this ray bifurcates again on fourteenth or sixteenth plate, the 

 outer division dividing again about the same distance above, making 

 six arms to this ray. 



The other rays, so far as can be seen from the only specimen we 

 have seen, have only a single brachial plate, which is a little longer 

 than the radial below, pentagonal, and supports on its upper angles 

 two stout arms, which divide first on the sixth or seventh plate, the 

 inner division continuing simple to its extremity, while the outer 

 one divides twice more on the tenth to the twelfth plate, making 

 eight arms to each of these rays, or thirty-eight to the entire indi- 

 vidual. 



Arms composed of short quadrangular joints, rounded exteriorly, 

 giving off rather delicate pinnules from their inner margins. Anal 

 series unknown. Column rather slender, composed of round plates, 



