358 PALAEONTOLOGY OF ILLINOIS. 



for the reception of a rather large round column, but not 

 expanded or provided with a rim around the lower margin ; 

 basal pieces rather large, wider than high, and hexagonal 

 in outline. First radial pieces large, about as wide as long, 

 hexagonal and heptagonal in form. Second radials about 

 half as large as the first, and regularly hexagonal. Third 

 radials of nearly the same size of the second, heptagonal 

 and hexagonal in form, arid supporting on each of their 

 superior sloping sides a secondary radial of somewhat 

 smaller size. The latter pieces curve outward, to form 

 with the upper anal and inter-radial pieces, the commence- 

 ment of the spreading disc; while each bears on its outer 

 sloping side, in direct succession, a series of three or four 

 large brachial pieces, leading out to the margin of the disc, 

 where the last one supports an arm ; and on the inner slop- 

 ing side there is a tertiary radial, giving origin to a series 

 of brachial pieces, leading to an arm on one side, as before, 

 while on the other sloping side it supports a quaternary 

 radial, and so on, until each primary division has in this 

 way thrown off alternately on each side from five to six, 

 or sometimes seven arms, thus making about twelve or 

 more arms to each of these main divisions, or near twenty- 

 four to each ray, and about one hundred or more arms to 

 the entire series. Arms slender and rising from the mar- 

 gins of the disc. 



Anal pieces near thirteen, the first being nearly as large 

 as the adjacent first radials, a little longer than wide, and 

 hexagonal in form; above this there are two smaller hex- 

 agonal pieces in the second range and three in the third 

 and fourth, with a few smaller pieces above. Interradials 

 about nine to eleven in each space, the first being rather 

 smaller than the second radials, hexagonal in form, and 

 supporting two smaller pieces in the second range, two in 

 the third, anjd two in the fourth, with a few irregularly 

 arranged smaller pieces extending up between the lateral 

 brachial pieces of the two adjacent rays. There are also 



