A MONOGRAPH OF THE EXISTING CRINOIDS 277 



Actinometra echinoptera var. mendionalis (part) Hartlaub, Mem. Mus. Comp. Zool., vol. 27, 



No. 4, 1912, p. 426 (Barbados); pi. 10, fig. 1. 

 Actinometra echinoptera var. tneridionalis-carinata (part) Hartlaub, Mem. Mus. Comp. Zool., vol. 



27, No. 4, 1912, p. 435 {Blake station 156). 

 Comactinia echinoptera (part) H. L. Clark, Univ. of Iowa Monographs; Bull. Lab. Nat. Hist., vol. 



7, No. 5, first ser., No. 15, April 1918, p. 8 (station 7). 



Diagnostic features. — There are never more than 10 arms; the cirri are rather 

 long and slender with 12-15 (usually 13-14) segments, of which the fourth is from 

 two and one-half to three times as long as its proximal width and the following de- 

 crease in length so that the penultimate is about as long, or not quite so long, as 

 broad; the fifth and following have a small, though prominent, sharp subterminal 

 dorsal spine; the first 2 segments of P2 and P3 are produced dorsally into high and 

 conspicuous carinate processes. The animal is rather slender; the arms are from 70 

 mm. to 90 mm. long, and the cirri are 10 mm. long. 



An examination of the cirri and of the bases of P2 and P3 will distinguish this 

 species at once from Comactinia meridionalis, which it resembles in size and in the 

 number of arms. 



Description. — The centrodorsal is a thin flat disk. The small cirrus sockets are 

 arranged in a single crowded marginal row, usually 5 to each radial division. 



The cirri are XV-XX, 12-15 (most commonly 13 or 14), 10 mm. long. The 

 first segment is short, the second is half again as broad as long to nearly square in 

 lateral view, the third is about twice as long as its terminal diameter, the fourth is the 

 longest, two and one-half to three times as long as its proximal diameter, and the 

 fifth is a transition segment, not quite so long as the fourth, with a dark band about its 

 center. The following segments gradually decrease in length, the antepenultimate 

 being very slightly longer than broad, or squarish, and the penultimate squarish or 

 not quite so long as broad. The second to sixth segments are slender, moderately 

 constricted centrally with prominent articulations, the following becoming rather 

 strongly compressed laterally (the outer portion of the cirri therefore becoming broader 

 in lateral view) and progressively less and less constricted centrally. The transition 

 and following segments have a small, though prominent, sharp subterminal dorsal 

 spine. The opposing spine is slightly marked, median in position, arising from the 

 entire dorsal surface of the penultimate segment. The terminal claw is somewhat 

 longer than the penultimate segment (about as long as the antepenultimate), moder- 

 ately stout and moderately curved, the curvature being strongest in the basal portion. 



The ends of the basal rays are visible as rather prominent tubercles in the angles 

 of the calyx. 



The radials are entirely concealed, or just visible over the ends of the basal rays; 

 they are separated distally. The IBrj are short, nearly four times as broad as long, 

 the proximal edge convex, not in contact basally, rounded and widely free laterally, 

 the sides of adjacent IBrj making with each other an angle of about 90°. The IBrj 

 (axillaries) are triangular, the anterior angle somewhat produced, about one and one- 

 half times as broad as long, the very short lateral edges making an obtuse angle with 

 those of the IBri. 



Arms 10, from 70 mm. to 90 mm. long. The first brachial is short, slightly wedge- 

 shaped, about three times as broad as the exterior length, entirely separated from its 



