136 Cincinnati Society of Natural History. 



The awl-shaped rays, and the spines borne by the second row of bra 

 chials, at once distinguish this species from all others yet described. 



Locality and position: Kaskaskia (Chester) Group, sub-carbonifer- 

 ous, Pulaski county, Kentucky. 



Pterotocrinus bifurcatus, n. sp. 

 Plate XL, fig. la. upper, \h basal, \c side view, natural size. 



Basals — Two pentagonal, deeply excavated centrally for the colum- 

 nar pit, and which bears a prominent carina at its edges. They are 

 much thickened in this region, and slope away rapidly to the first 

 radials, 



Radials — First series five, the two on the azygos side heptagonal, 

 wider than high, laterally excavated for the reception of the azygos 

 plate, which they completely embrace, and much resembling, in their 

 general features, the same plates in the P. acutus herewith described. 



The opposite first radial is beptagonal, somewhat widei than high, 

 and has a slight angle on the inner side, which points to the line of 

 junction of the basals. The other two first radials are hexagonal, 

 wider than high, and resemble the anterior one in outline, save that 

 they abut upon the basals by a single side instead of two. 



The radials of the second series are irregularly quadrangular, ten 

 in number, small, closely united or nearly anchylosed to the first, and 

 cover a little more than one half the upper side. They are enclosed, 

 laterally, by the outside pairs of third radials. 



These latter are twenty in number, irregularly quadrangular, and 

 nearly as high as wide. Their position in reference to the adjacent 

 plates is the same as that of the other crinoids of this genus. The 

 ratio of height to width is less that in any of the other species de- 

 scribed in this paper. 



Azygos inece — This is quadrangular, the inner faces being straight, 

 and meeting the basals in a sharp angle at their line of junction, as in 

 P. acutus herewith described. The other sides are convex and em- 

 braced by the first radials. 



Brachials — Of these there are sixty, in series of threes, resting upon 

 the third radials, and differing from them very slightly in form. 

 There is evidence in one or two cases that these plates were tuber- 

 culated, though very slightly. 



Arms — Twenty, composed of a double row of alternately interlock- 

 ing plates, about forty to each side, each of which bears a stout pin- 

 nule. The arms are thick at the base, and taper very gradually, as 

 the plates shorten towards their extremities. As in the other species, 



