BULLETIN NO. 2. 27 



POTERIOCEINUS SPINULIFEROUS. (sp. nOV.) 



Body of medium size, short, width three times as great as the 

 height to the top of the first radials ; base depressed, under-basals 

 small and concealed under the first columnar joint. Column ob- 

 scurely pentagonal near its upper extremity, becoming round be- 

 low, slender and composed of alternate thin and thicker joints 

 near the base, beyond which it is unknown. 



Basal plates forming a flat disk with slightly curving angles 

 above and below, so that the body if detached would rest on the 

 central portion of these plates. First radials short, pentagonal, 

 twice as wide as high, angular below to fill the depressions be- 

 tween the basals. Under a good lens they show rude striations 

 around their lower borders, with a slight depression in the upper 

 margin, forming a well defined suture between them and the sec- 

 ond radials. Second radial series on four of the rays as long as 

 their greatest breadth below, angular in front, and compressed at 

 the sides, the apex produced into a rather prominent node, and 

 support on the upper angles the first divisions of the rays. The 

 right antero-lateral ray divides again on the sixth plate, and 

 again on the sixth and twelfth, while the left antero-lateral 

 divides the second time on the sixth plate, and the outer division 

 again on the seventh or eighth plate, while the inner one contin- 

 ues simple beyond the second bifurcation. 



The anterior ray has five radial plates, the flrst corresponding 

 in form and size with those of the other rays, the second is quad- 

 rangular, longer than wide, narrower above than below, the third 

 and fourth are quadrangular, about half as long as wide, the fifth 

 is about as long as wide, axillary and produced into a strong node 

 like the axillary plates of the other rays. 



The right division of this ray divides again on the tenth plate, 

 while the left continues single as far as it is preserved. 



All the axillary plates of the arms are nodose, and longer than 

 the others, which are slightly wedge-formed and give off strong 

 pinnules from their longer sides. 



Position and locality : Chester limestone, near Columbia, Mon- 

 roe county. 111. 



No. 2492 of the Illinois State collection. 



Collector, A. H. Worthen. 



