174 PALEONTOLOGY OF ILLINOIS. 



and inferior (inner) margins distinctly beveled, like the basal 

 pieces. Second radials about half as large as the first, from 

 the truncated outer ends of which they extend out nearly hori- 

 zontally, or even decline slightly below the horizon of the base, 

 presenting a pentagonal inferior view, and curving strongly 

 upwards on each side to connect with the vault pieces. Inter- 

 radials rather small, hexagonal or heptagonal, and rising ver- 

 tically from the upturned edges of the first radials. Anal 

 piece not much larger than the interradials, and apparently 

 octagonal. 



The arms, after the first bifurcation on the second radial 

 pieces, extend out horizontally, or even decline a little at 

 first, and then curve gradually upwards; they all bifurcate 

 regularly again on the second piece, the inner subdivisions 

 generally bifurcating a third time on the second piece, while 

 one, or sometimes two of these subdivisions divide again, so as 

 to make 37 (probably sometimes 40) arms in the entire series. 

 The arms are rounded on the outside, gradually tapering; and 

 immediately after the last division, each is at first composed of 

 one, two, or three wedge-formed pieces, beyond which they soon 

 pass into a double series of small alternating pieces, supporting 

 on the inner side a double row of thick, closely-arranged tenta- 

 cles. 



The summit is composed of various formed plates, each 

 of which rises in the middle into a short spine or prominent 

 tubercle. These pieces extend out from the vault, so as to 

 form the summit of each ray nearly to the second bifurcation. 

 The anal opening is small, lateral and surrounded by small, 

 rather protuberant pieces. Entire surface finely and rather 

 obscurely granulose. 



We are under obligations to Mr. Charles Wachsnmth, of Burlington, Iowa, 

 for the use of the beautiful, unique specimen from which our figure and descrip- 

 tion of this species have been made out. It is one of the finest, if not the finest 

 specimen of Platycrinus ever found, being so completely detached from the 

 matrix that almost every part of the skeleton, excepting the column, which is 



