INVEETEBRATES. 298 



Radials pentagonal, nearly twice as wide as high, with a sharp 

 node in the center corresponding with those on the subradials, with 

 distinct ridges extending obliquely from the nodes to meet those on 

 the subradial plates. 



Brachials two, the first quadrangular, half as long as wide, the 

 second pentagonal, about as long as wide, and sharply angular 

 above, supporting on its upper sloping sides the first arm plates, 

 which are only preserved to the seventh plate above the last brachial 

 in our specimen. The brachials and the arm plates as far as they 

 are preserved are spine-bearing. 



Two anals are preserved, the first is about half as large as the 

 large snbradials between which it rests, the second is smaller and 

 rests on the truncated upper margin of the left posterior subradial, 

 and both ornamented like the subradials. 



This species is apparently related to Z. Siimpsoni of 8. S. Lyon, 

 but differs conspicuously from that, in the number of its brachials, 

 as well as in minor details. 



Position and locality: Chester limestone, Monroe county, 111. 



No. 2,445, Illinois State collection. 



POTEEIOCKINUS CoLUMBIENSIS, Worthen. 



PL XXIX, Fig. 6, 



Poteriocrinus Colunibiensis, WOETHEN, February, 1882. - 



Bulletin No. 1, of the Illinois State Museum of Natural History, p. 22. 



Body small, turbinate, rapidly spreading from the base to the 

 summit of the radial plates. 



Basal plates small, projecting about half their length beyond the 

 column. Subradials about as high as wide, three hexagonal, and 

 two on the posterior side a little larger and heptagonal. 



Eadials pentagonal, a little wider than long, except the one on 

 the right posterior ray, which is narrower and nearly quadrangular. 

 Brachials about twice as wide as long, rounded and constricted in 

 the middle, pentagonal, supporting on their upper sloping sides two 

 arms that continue single to their extremities. 



Arms composed at their base of long, rounded joints, twice as 

 long as wide, but decreasing in length above, the joints projecting 

 laterally for the support of strong pinnules which are given off from 

 each plate on alternate sides. Arm plates slightly cuneate in form, 

 and the lateral projections give a zigzag appearance to the arms. 

 Pinnules composed of round joints that are twice as long as wide 

 where they join the arms. 



