CLARK : CRINOIDS. 245 



to those given, two other types which should be raised to generic rank, but, as 

 they are both West Indian and do not occur in the territory where the free cri- 

 noids considered here are found, it has seemed desirable to leave them for a report 

 upon West Indian species. 



Key to the genera of Antedonidae. 



Pinnule ambulacra plated. 

 a. pinnules stout and prismatic, stiff, and closely set ; radials and costals, and 

 lower brachials, strongly flattened laterally (i. e. " wall-sided "). 

 b. first pinnule similar to, but shorter than, those following ; cirri very 

 long, with more than 80 segments ; the distal pinnules extend for 

 several millimeters beyond the terminal brachials, which are ab- 

 ruptly recurved. 



c. centro-dorsal long-conical or columnar, the cirri in 5 double verti- 

 cal rows ; cirri stout; 10-20 arms 



Asterometra (Antedon tnacropoda A. H. Clark). 



cc. centro-dorsal thick-discoidal or columnar, the cirri without 



definite arrangement, or in 15 more or less defined vertical rows ; 



cirri slender ; 10-30 arms 



Ptilometra (Comatula macronema J. Muller). 

 bb. first pinnule longer than those following ; the distal pinnules short, 

 not extending beyond the terminal brachials, which are not incurved, 

 c. first pinnule markedly larger, stouter, and longer than those fol- 

 lowing, composed of comparatively few large, stout segments ; 

 cirri elongate, slender, always spiny, with more than 25 seg- 

 ments ; genital pinnules not differentiated ; 10-30 arms . . . 

 Thalassometra (Antedon villosa A. H. Clark). 

 cc. first pinnule longer, but smaller and more slender than those 

 following, with much more numerous and shorter joints ; cirri 

 short, stout, and smooth, with less than 30 segments ; genital 

 pinnules always more or less expanded ; 10-50 arms .... 

 Charitometra (Antedon incisa P. H. Carpenter). 

 aa. pinnules rounded-carinate, the genital pinnules much expanded ; costals 

 and lower branchials laterally compressed, with concave sides, the former 

 with broad, thin, flange-like latero-posterior borders ; cirri short, stout, 



and smooth ; 10 arms 



Poecilometra (Antedon acoela P. H. Carpenter). 

 aaa. pinnules cylindrical, stiff and spine-like, well separated, the first small, 

 short, and weak, with squarish joints ; proximal segment of lower pin- 

 nules (especially the first) enormously expanded ; cirri spiny ; 10-50 



arms Calometra (Antedon callista A. H. Clark). 



aaaa. proximal pinnules slender, elongate, cylindrical, stiff, with much elon- 

 gated segments, the first shorter than the following; distal pinnules 

 strongly prismatic ; costals and lower brachials rounded, free laterally ; 



20-30 arms 



Stylometra (Antedon spinifera P. H. Carpenter). 



