180 PALAEONTOLOGY OF ILLINOIS. 



The body in this genus is usually obconical, with the five 

 basal pieces united «so as to form a more or less depressed pen- 

 tagonal cup. Three of the five subradials are of the same form, 

 and two on the anal side are more variable, and generally have 

 each one or two sides more than the others. The five first 

 radials are usually larger than the others, and connect with 

 each other laterally, so as to form a part of the walls of the 

 body; four of them are pentagonal, and alternate with the sub- 

 radials, and the other generally hexagonal and often, though 

 not always, raised with its summit above the others, while its 

 base usually rests directly upon the upper truncated margin of 

 one of the subradials. 



The succeeding radial pieces vary in number, size and form 

 in the various species, or even in the different rays of the same ; 

 there being sometimes as many as thirteen or more in one ray, 

 and only from two to about five in the others. All of the 

 radial pieces above the first series are free; or, in other words, 

 those composing the different rays are not connected laterally, 

 so as to form a part of the walls of the body. The anal pieces 

 are somewhat irregular in their arrangement, but generally one 

 of the first two rests between the superior sloping sides of the 

 two irregular subradials, while the other is supported upon the 

 truncated upper side of one of the subradial pieces; above these 

 there are from two to four other anal pieces connected with 

 the base of the proboscis. 



The vault or summit of the body is enormously developed in the form of a 

 great cylindrical, or ventricose trunk, generally at least as wide as, or in Cselo- 

 crinus much wider than, the cup below, and nearly or quite as long as the 

 arms, while its single opening is said to be located at its upper extremity.* 

 DeKoninck and Lehon think it was, in some species, merely protected by a 

 soft integument, but in all the various species in which we have seen this part, 

 it was composed of numerous small, very regular, close fitting, hexagonal plates, 



* We follow Austin and others, in giving the upper extremity of the proboscis as 

 the position of the opening of the summit, not having seen this opening in any of the 

 specimens of this genus we have examined. 



