gig BULLETIN 82, UNITED STATES NATIONAL MUSEUM VOLDMB 1 



between brachials 4+5 and 7+8; right anterior, between brachials 4+5, 7+8, and 

 10+11; right posterior, between brachials 3+4, 6+7, and 9 + 10. The length from 

 the proximal edge of the first brachial to the syzygy at 7 + 8 is 12.0 mm. 



The sculpture of the syzygial faces in this species is unique. Laterally and dorsally 

 the central canal is bounded by a high ridge of moderate width; from this ridge there 

 extends to the dorsal margin of the joint face in the dorsoventral line another ridge 

 which at first is about as broad as the ridge from which it springs, but on the outer 

 side gradually broadens to a slight degree. Two similar ridges extend outward, one 

 from either end of the laterodorsal ridge about the central canal, making with the 

 median ridge an angle of about 45°, or about a right angle with each other. Just 

 beyond these lateral ridges, entirely unconnected with the ridge about the central 

 canal, separated from the lateral ridges by a ligament space about the same shape 

 and size as the two lateral ridges, are two more ridges, slightly broader than the others; 

 each has a very narrow fan-shaped space beyond it. Beyond these two ligament 

 spaces, the distal borders of which are approximately at right angles to the dorsoventral 

 axis of the joint face, are two large obsolete muscular fossae which are about as high 

 as the distance between their proximal borders and the dorsal edge of the joint face. 

 These are rounded triangular in shape; inwardly each rises somewhat, forming two 

 parallel, very inconspicuous, low and well-rounded ridges, which are interiorly sepa- 

 rated by a shallow rounded groove. This groove becomes more accentuated just 

 beyond the central canal, where it separates the inner ends of the inner pair of ridges. 

 The inner ends of the ligament spaces just beyond these ridges are bounded by the 

 ridges bordering interiorly the muscular fossae. There is a deep intermuscular notch 

 the sides of which make an angle of from 60° to 90° with each other. The ridges on 

 the syzygial faces are high, and consequently the ligament fibers are long, appearing 

 in dorsal view almost or quite as long as those of the neighboring dorsal ligaments. 



All of the pinnules are present. Pi, which arises from the right side of the second 

 brachial on 4 arms, is about 16 mm. in length; the fu-st segment is slightly trapezoidal, 

 and, as viewed from the side, about half again as long as broad ; the second is between two 

 and a half and three times as long as broad, 2.3 mm. in length. The following seg- 

 ments are similar, but proportionately somewhat longer. The pinnule is moderately 

 stout, like the proximal pinnules of the large species of Psathyrometra, and is some- 

 what compressed laterally. The first segment increases somewhat in width distally, 

 the second decreases slightly, and the third also decreases slightly, more especially 

 in the prox-imal half; from that point onward the pinnule tapers very gradually. 



P2 is 15 mm. long, with 10 segments, and resembles Pi; the fourth segment, which 

 is the longest, is about three and a half to four times as long as broad, and the fifth 

 is about the same; but the sixth and following are only about twice as long as broad, 

 or slightly less. 



Only the bases of the following pinnules are preserved; they appear to become 

 gradually shorter and more slender, the second segment decreasing rapidly in length 

 and progressively decreasing more and more rapidly in distal width, on the pinnule 

 of the ninth brachial being not quite so long as its proximal width and slightly trapezoi- 

 dal, so that the following segments must have been very slender. 



The surface of the disk is more or less mutilated and concealed. The disk re- 

 sembles that of Atelecrinus, and is comparatively small and compact, its ventral surface 

 reaching the height of the base of the ninth brachial. The ventral surface of the disk 



