CLARK] NEW GENERA OF RECENT FREE CRINOIDS 347 



tubercular, the former well-separated laterally. 



(n) Cyllometra 

 cc. Centro-dorsal conical, the elongate and slender cirri in more 

 or less definite vertical rows ; costals and lower bra- 

 chials strongly tubercular, in close apposition, and 



sharply "wall-sided." (12) Perometra 



AA. Pinnule ambulacra plated. 



a. Pinnules stout and prismatic, closely set; costals (also distichals and 

 palmars when present) and lower brachials sharply 

 "wall-sided." 

 b. Distal pinnules extend several millimeters beyond tip of arm, which 

 is sharply recurved; first pinnule of the same char- 

 acter as the following, but much smaller ; cirri very 



long with 80 to 130 segments (13) Ptilometra 



bb. Distal pinnules very short, not extending beyond tip of arm, which 



is not incurved. 



c. First pinnule much enlarged, composed of a few large, stout 



segments; genital pinnules not differentiated; cirri 



long, slender, with 25 to 90 segments, the distal 



always spiny ( 14) Thalassometra 



cc. First pinnule more slender than the following, longer, com- 

 posed of a large number of small joints; genital pin- 

 nules more or less expanded ; cirri short and stout, 

 with less than 30 segments without dorsal spines. 



(15) Charitometra 

 aa. Pinnules prismatic ; costals deep, with concave sides and a prominent 

 latero-posterior thin flange-like margin; genital pin- 

 nules much expanded; cirri short, stout, and smooth. 



(16) Pcecilometra 



aaa. Pinnules slender and cylindrical, well separated and thorn-like; 



costals rounded; cirri distally spiny. ..(17) Calometra 



1. ZYGOMETRA, gen. nov. 



Centro-dorsal discoidal, bearing one to three rows of marginal 

 cirri; cirri very variable, but always stout, with 15 to 50 segments, 

 with or without dorsal spines ; the segments are, however, always 

 short (almost always broader than long), and very uniform in size; 

 disk always plated, but pinnule ambulacra naked; costals united by 

 syzygy, always well rounded, well separated laterally, never carinate ; 

 ten to ninety or more arms, distichals 4 (3 + 4) (almost never 2), 

 the subsequent series either 2 or 4 (34-4); lower pinnules more or 

 less elongate (but not markedly so), the basal segments often some- 

 what carinate ; distal edges of costals and brachials often everted or 

 overlapping; brachials always wider than long. 



Color in life yellow, brown, purple, or red, usually more or less 

 definitely banded. 



Type of the genus. — Antedon microdiscus Bell, 1884. 



