INVERTEBRATES. 87 



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, penta- 

 gonal, twice as wide as high, angular below to fill the depres- 

 sions between 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 second 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 prom- 

 inent 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 continues simple beyond the second bifurcation. 



The anterior ray has five radial plates, the first correspond- 

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

 quadrangular, 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. 



Collector, A. H. Worthen. 



No. 2492 of the Illinois State Museum. 



POTERIOCUIXUS ULRICHI. (sp. 11OV.) 

 PI. XVII, Fig. 2. 



Calyx below the second radial plates cup shaped, about twice 

 as wide as high. Base concave, and underbasals concealed by 

 the column. Basals on the posterior side pentangular slightly 

 projecting on their upper margins, leaving a well defined suture 

 between them and the second radials. The second radials are 



