CRINOIDS AND BLASTOIDS. 181 



of the ray, thirty in all, with occasionally an additional one in 

 one or both posterior rays. The arms are proportionately 

 heavier than in other species of the genus, but taper rapidly at 

 their tips. They are composed of a double series of very short 

 interlocking pieces, with deeply indented suture lines so as to 

 give to the back of the arms a file-like appearance. Pinnules 

 strong, continuous, composed of elongate joints. 



Interradials 7 to 9 in four or five ranges; the first plate 

 smaller than the first radials. This is succeeded by two, rarely 

 three, plates of nearly the same size, and two or three ranges 

 of smaller plates. Azygous interradius wider and easily distin- 

 guished. It has always three plates in the second range, of 

 which the middle one is an anal, higher than the first radials 

 and fully as wide. There is a second anal plate in the third 

 range, which is but little more than half the size of the first. 

 Succeeding plates small and more or less irregular. Anal aper- 

 ture placed at the end of a very short, wart-like, somewhat 

 tubular and almost central protuberance, which is directed up- 

 wards, and surrounded by small spiniferous plates. The plates 

 at the azygous side are similar in proportion but greater in 

 number than at the other sides. Vault slightly elevated and 

 rounded, with small depressions toward the interradial spaces. 

 It is composed of numerous, very small tumid pieces, among 

 which the summit plates are with difficulty distinguishable. 



Surface of plates convex or slightly angular, covered with 

 ridges passing from plate to plate. The ridges following the 

 radials pass into the arms, growing sharper and higher on 

 approaching the arm bases. 



Column large, round, joints short, of uniform diameter; cen- 

 tral opening small, round or obscurely pentagonal. 



This is one of the most characteristic species of the Le Grand 

 beds, and we take pleasure in naming it in honor of G. F. 

 Kirby, Esq., of Marshalltown, Iowa, the President of the Le 

 Grand Quarry Co. 



Geological position, etc.: Same as the last species. 



Our own collection. 



