EEVISION OF PALEOZOIC STELLEKOIDEA. 265 



in proportion to breadth. In a specimen wdth a disk measuring 

 0.25 inch in breadtli, the diameter of tlie arms near the disk is only 

 0.05 inch. None of the specimens show the entire length of the arms, 

 though some fragments of them were seen lying detached in the 

 matrix, about 0.55 inch in lengtli, without being complete at either 

 end. From the breadth and gradual taper of these, it would seem 

 probable that when entire they may have been 0.75 to 1 inch in length. 

 Tlieir impressions in the matrix give no indications of a longitudinal 

 furrow along the under side, but show that there were about six 

 pairs of arm pieces in a length of 0.16 inch. These pieces appear 

 to be nearly though not exactly opposite, and each one provided 

 below with a comparatively large, round, deep pit, or pore, near 

 the middle of its anterior side. Along their lateral margins there 

 appear to be impressions in the matrix of very small spines (one to 

 each arm piece), though if such, they must have been extremely 

 short. Impressions of the upper side of the slender arms show 

 them to have been somewhat rounded above, with the nearly square 

 arm pieces slightly alternating. Some of the impressions seem to 

 show traces of central pores or pits, one at the middle of each pair 

 of pieces, though in others no traces of these are visible." 



Formation and locality. — Common as molds in a fine impure 

 sandstone and in the famous crinid bed at Crawfordsville, Indiana, 

 in the Keokuk formation of the Mississippic. 



There are two specimens (No. 6) of this species in the Wachsmuth 

 collection at Harvard University. At Yale University there are 

 four specimens. 



Family CHOLASTERID.E Worthen and Miller. 



Cholasteridpe Worthen and Miller, Geol. Surv. Illinois, vol. 7, 1883, p. 328. 



Original deiinition. — Cholaster "is so widely different from those 

 heretofore discovered that we think it belongs to a distinct family, 

 which might very appropriately be designated the Cholastcridie, 

 but until other specimens have been found showing other parts 

 of the body, we prefer to let the family remain undefined," 



Contains the genus : 



Cholaster Worthen and Miller. 



Genus CHOLASTER Worthen and Miller. 



Cholaster Worthen and Miller, Geol. Surv. Illinois, vol. 7, 1883, p. 328. — 

 Gregory, Proc. Zool. Soc. London for 1896, 1897, p. 1040. 



Onginal description. — Dorsal side alone known. "Body trun- 

 cated pentagonal, central area circular, deep and largo in propor- 

 tion to the rays; rays distant, small, short and abruptly truncated. 



