CRINOIDS AND BLASTOIDS. 183 



cation of the outer branch in a posterior ray, giving normally 

 6 ultimate arms to the ray, or 30 in all. The free arms are 

 biserial, slender, tapering very gradually; the arm pieces pro- 

 portionately longer and narrower than in Jt. kirbyi, and the 

 back of the arms more rounded and smoother. Pinnules strong, 

 not so closely packed as in the last named species. 



Interradials 8 to 10; the first one half as large as the first 

 radials, and the two in the second range almost equaling it in 

 size. There are several more ranges of plates above, which are 

 irregularly arranged and decrease in size upwards. The anal 

 interradius is wider. It contains a row of anal plates, longitu- 

 dinally arranged, which rest upon the truncate upper face of the 

 first interradial, and extend up to near the anal aperture, 

 forming a kind of ridge, which is readily distinguished from the 

 surrounding slightly depressed interradial plates. The first anal 

 plate is as large as the first radials, the interradials on either 

 side of it smaller than the corresponding plates at the four 

 other sides. Anus excentric, protuberant, tube-like, composed 

 of rather large plates; opening directed upwards; 



Ventral side rising somewhat above the dorsal cup, depressed 

 in the interradial spaces, and composed of small, irregular convex 

 pieces. Summit plates very indistinct, if represented at all. 



The surface of the calyx is marked by rounded radiating 

 ridges, which are continuous along the radial series, and extend 

 into the arms. The ridges vary somewhat in prominence among 

 specimens, and in some are almost entirely confined to the 

 radial series, giving to the calyx a pentagonal outline ; while in 

 others they also pass to the basals, interradials and anals. 

 The plates as a rule are convex, and the suture lines well de- 

 fined. 



Column small, round, composed of alternate joints; perfora- 

 tion small, apparently round. 



Geological position, etc. : Kinderhook beds of the Lower Car- 

 boniferous, Le Grand ; also, Burlington, Iowa. 



Our own collection. 



