INVERTEBRATES. 299 



ation, beyond which they continue simple to their extremities, 

 making four arms to each ray. The arm joints are all slightly 

 wedge-formed, and quite short above the second division, and sup- 

 port strong pinnules, which are given off from the longest sides of 

 the joints. 



The anal side presents an anomalous feature that I have not ob- 

 served in any other species of Poteriocrinus. In addition to the 

 ordinary anals placed as is usual in this genus, there is a pentagonal 

 plate about as long as the radials, intercalated between the right 

 posterior radial and the subradial below, elevating the lower angle 

 of this radial to a level with the summit of 'the other radial plates. 

 This may be only an abnormal development, and I was at first in- 

 clined to regard this as only a variety of P. venustus, but its shorter 

 brachials and arm-plates, and different mode of bifurcation of the 

 arms, seems to afford good grounds for considering it as a distinct 

 species. 



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



No. 2,448, Illinois State collection. 



POTERIOCBINUS pROPiNQUus, Worthen. 



PL XXIX, Fig. 9. 



Poterionrlnus propinqmis, WOKTHEN, Feb., 1882. 



Bulletin No. 1, of the Illinois State Museum of Natural History, p. 26. 



Body below medium size, obconic or bell-shaped, spreading rather 

 rapidly from its truncated base to the summit of the radial plates, 

 where it is nearly twice as wide as high. 



Basals about half as long as wide above their junction with the 

 column, forming a shallow, pentagonal cup. 



Subradials on the anterior side hexagonal, length and breadth 

 about equal, their upper angles extending up about half the length 

 of the radial plates. Kadials one-fourth to one-third wider than 

 high, pentagonal, with their upper margins squarely truncated for the 

 reception of the brachial plates. 



Brachials widest at their lower margins, not quite as long as wide, 

 constricted in the middle, and sharply angular above, where they 

 support the first divisions of the rays. Arms four to eight to the 

 ray, so far as can be seen from the specimen under examination. 

 The left posterior ray divides the second time on the eighth or 

 ninth plate above the brachial, beyond which the arms appear to 

 be simple to their extremities. The right antero-lateral arm bifur- 



