288 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



to the antepenultimate which is four times as long as the median diameter and the 

 penultimate which is wedge-shaped, increasing in diameter distally, and twice as 

 long as its median diameter. The outer segments are laterally compressed. Under 

 high magnification their distal dorsal edges are seen to be armed with fine spines 

 and gabled in the middle, though the point of the gable is not produced. The oppos- 

 ing spine is large and prominent, conical and sharp, directed obliquely forward. The 

 terminal claw is shorter than the penultimate segment, slender and evenly curved. 



The radials are concealed by the centrodorsal except in the interradial angles, 

 where they are produced anteriorly and separate rather widely the bases of the 

 IBri as in Comatilia. The IBri are very short, from six to eight times as broad as 

 long, with the proximal border more or less overlapped by the centrodorsal, the sides 

 curving inward distally, and the distal border a very broad reentrant obtuse angle. 

 The axillaries are much wider than long, the lateral edges very short and rapidly 

 converging, making with the similarly converging sides of the IBri somewhat less 

 than a right angle, the proximal border a broadly obtuse angle. 



The 10 arms are 12 mm. long. The brachials resemble those of Comatilia; their 

 sides are rather strongly concave, and their edges and dorsal surface are finely spinous. 

 The earlier brachials are about as long as broad, but distally they become elongated 

 and four or five times as long as broad. 



Syzygies occur between brachials 3+4, 8 + 9, 12+13, and distally at intervals 

 of 2 muscular articulations. 



The mouth is centra! and the anal tube marginal. 



P, is long and very slender, with much elongated segments, the longest five or 

 six times as long as broad, the distal becoming shorter, centrally constricted with 

 finely spinous ends. The terminal comb consists of 3 very large lance-head-shaped 

 teeth, which are much longer than the diameter of the segments which bear them. 

 Apparently P,, P^, and P2 bear combs; P^ and P3 bear the first genital glands. 



Locality.— Off Frederiksted, St. Croix (Santa Cruz), Virgin Islands; about 91-183 

 meters; Th. Mortensen, February 8, 1906 (1, type specimen, C. M.). 



Remarks. — It gives me great pleasure to name this curious little species in honor 

 of its discoverer, my friend Dr. Th. Mortensen. 



Although so very small, the single known individual is evidently adult, having 

 swollen genital glands. The exceedingly attenuated cirri represent a highly special- 

 ized character, for the first cirri to appear in all pentacrinoids are relatively stout 

 with short segments — at least in the forms with elongated cirrus segments those in 

 the cirri of the pentacrinoids are much shorter than those in the cirri of the adults. 

 The terminal combs on the oral pinnules are quite unique in having only 3 teeth, 

 and these teeth are remarkable for their extraordinary development, recalling the 

 teeth in the very long combs of Comatonia cristata. The position of the second 

 brachial syzygy, which is between brachials 8 + 9 instead of between brachials 9 + 10 

 as usual, is noteworthy. 



Genus COMATONIA A. H. Clark 



Antedon (part) P. H. Carpenter, Bull. Mus. Comp. Z06I., vol. 9, No. 4, 1881, p. 155. 

 Actinometra (part) Hartlaub, Mem. Mus. Comp. Z06I., vol. 27, No. 4, 1912, p. 280. 



