1881.] NATURAL SCIENCES OF PHILADELPHIA. 351 



the bod}^, as also the shortness and delicacy of the arms. It 

 differs from Agaricocrinua and Amphoracrinus in the form and 

 proportions of the body, in the arrangement of the plates, and in 

 the altogether different arm strnctnre. 



We place Meek and Worthen's snbgenns Gcelocinnus, -which, had 

 been previousl^^ described, successively, under Actinocrinus, Am- 

 phoracrinus and Sjjh^rocrinus, as a synonym under Dorycrinus^ 

 the only known species being a somewhat aberrant form, but not 

 sufficiently distinct even to make it a subdivision. 



Generic Diagnosis Calyx broadh' turbinate or subglobose, 



truncate at the base, and deeply sinuate at the interradial spaces, 

 the sinus at the posterior side much deeper and wider, and 

 extending up to the vault, thereby giving to the body a decidedly 

 pentalobate aspect, with a strongly expressed bilateral symmetry. 

 Dome from one-fourth to one-half the height of the body, strongly 

 convex, composed of comparatively few and large plates, fre- 

 quently armed with one to six spines. Plates sometimes cor- 

 rugated, but not striated, and all more or less convex or nodose. 



Basals three, equal, short, in the t3q3ical forms of the genus 

 abruptly spreading, the lower exterior margins extending almost 

 at right angles to the axis of the fossil ; deeply sinuate at 

 the sutures, but sometimes forming a continuous ring. Primary 

 radials 3X5; the first as large or larger than the second and 

 third together; the second much narrower than the first, but 

 wider than high, quadrangular in outline, although sometimes (in 

 the same specimen) pentagonal or hexagonal, owing to the position 

 of the second series of interradials, upper and lower sides parallel; 

 the third more or less pentagonal, wider than high, wider in rays 

 with three or four arm bases than with two. The third radial, in 

 rays with only two arm openings, with 2X2 secondar}^ radials, 

 which support the arms, but in rays with three or four openings, 

 and consequently with tertiary radials, the secondary' radials 

 consist of a single series of plates, of which one or both are axillarj'. 

 In the latter case, the plate gives off 1 X 2 arm-bearing plates, in 

 the former another row of secondary radials, which support the 

 arms. The arm bearing plates, all around the body, are project- 

 ing, rounded toward their sides, and separated by a deep lateral 

 depression or sinus, which is deeper and wider between the main 

 divisions of the ray, and which at the space between the rays 

 forms a wide and deep gap. Dorycrinus has variously from 



