26 



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

 clined to regard this as only a variety of P. remistus, 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 dis- 

 tinct species. 



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



Illinois State collection. 



POTERIOCRINUS PROPINQUUS. N. SP. 



liody 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. Eadials 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 sim- 

 ple to their extremities. The right antero-lateral arm bifurcates the 

 second time on the eighth or ninth plate, the right branch sending 

 off two additional arms on the seventh, and again on the fourteenth 

 plate, while the left branch gives oft" another arm on the eighth or 

 ninth plate, beyond which it is not preserved. There are probably 

 eight arms to this ray. The other rays are not preserved beyond 

 the second bifurcation. The arms are composed of rather short, 

 wedge-formed joints, that give oft strong pinnules from their longest 

 sides. 



Anal area unknown. Column round, composed at ftrst of rather 

 even joints, with a thicker one intercalated at short intervals below. 

 The calyx of this species could not be readily distinguished from 

 several others that are found in the Chester limestone, but its long, 

 slender arms, and their mode of bifurcation, are its distinctive 

 characters. 



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

 Illinois State collection. 



