J 879.] NATURAL SCIENCES OP PHILADELPHIA. 349 



1860. Zeacrinus Meek & Worthen. Subgenus of Poteriocrinus. Geol. Rep. 

 111., vol. ii. p. 186. (Not Zeacrinus Schultze. Monog. Ecbin. 

 Eifel Kalk., p. 38.) 



General form of body with arms closed, terete or subcylindrical, 

 often contracted near the arm bases and spreading above ; Calyx 

 more or less depressed, low cup or basin-shaped, rarely turbinate, 

 with the basal portion sunken in and forming a deep concavity. 

 Arrangement of plates slightly unsymmetrical. 



Underbasals five (abnormally six), small, generally hidden in 

 the central concavity, and covered by the column. Basals five, 

 sometimes nearly equal, but more frequently showing a tendency 

 to irregularity on the posterior side. Radials five, pentagonal, 

 the upper side truncate, with a single brachial plate in each of the 

 four lateral ra} r s; the anterior ray, however, as a rule has one, 

 two, to six or more additional quadrangular brachials, and a bifur- 

 cating plate above, resembling in outline the single brachial of the 

 other rays. The latter plate is wide, rather short, and of the form 

 of the radials, but truncate below, and joining the entire upper 

 margin of the radial. 



Arms comparatively short, bifurcating, scarcely rounded on the 

 exterior, rarely angular; the bifurcating plates comparatively 

 larger and sometimes nodose. Ramifications only occur on the 

 two outer arms of the rays, and these arms have straight outer 

 margins throughout their length. The branches are given off at 

 regular intervals toward the inner side of the ray, and remain 

 single throughout. The arms are all of uniform thickness, and 

 their sides are sharply defined, and when closed they join so 

 neatly with each other that it appears as if they formed a solid 

 bod} r . Arm-joints much wider than long, with nearly parallel 

 sutures. Pinnulas short and slende.r, composed of six or more 

 angular joints directed to the interior of the crinoid, not given off 

 laterally. Arm furrows apparently covered by the infolding of 

 the pinnulse, not by alternating plates. 



There are from five to seven anal plates, alternately arranged in 

 two rows, the lower plate resting with one side against the sloping 

 right side of the posterior basal, the other against the right pos- 

 terior radial, in some species almost touching the underbasals. 

 The arrangement of the succeeding plates is very similar to that 

 of Woodocrinus, except that the portion of the anal area above 

 the line of the radials has a sharp triangular outline instead of 



