A MONOGRAPH OF THE EXISTING CRINOIDS 145 



description; localities), fig. 35, p. 196; Die Crinolden der Antarktis, 1915, p. 125 (shows char- 

 acteristic features of Anthometra adriani). 

 Oceanometra annandalei A. H. Clahk, Journ. Washington Acad. Sci., vol. 6, No. 17, 1910, p. 606 

 (listed) ; Unstalked crinoids of the Siboga-Exped., 1918, p. 151 (in key; range), p. 153 (references). — 

 Gisl£n, Zool. Bidrag Uppsala, vol. 9, 1924, p. 80, fig. 79, p. 81 (syzygial face); Kungl. Fysiogr. 

 Sallsk. Handl., new ser., vol. 45, No. 11, 1934, pp. 22, 23. 



Diagnostic features. — All the ossicles of the division series and the first two brachials 

 bear median keels and have smooth lateral borders which are not produced and a more 

 or less spinous dorsal surface; the dorsal surface of the earlier brachials is more or less 

 densely spinous. This is a rather slender species, with slender cirri; the 19-23 (usually 

 20) arms are 110-160 (usually 110-130) mm. long, and the cirri are 40-65 mm. long 

 with 62-79 segments. 



Description. — The centrodorsal is columnar with the tip truncated conical as in 

 Asterometra, 5 mm. high and about 5 mm. broad at the base. The cirrus sockets are 

 arranged in 10 columns, of usually three each, the columns of adjacent radial areas being 

 closely crowded and with the sockets more or less alternating, while the two columns in 

 each radial area are separated in the midradial line by a slightly concave median area 

 of about half their width. The polar area of the centrodorsal has five more-or-less 

 marked interradial ridges which terminate in five small tubercles about the apex. 



The cirri are XXX, 62-79, 65 mm. long, and comparatively slender. The first 

 three segments are approximately equal, short, about twice as broad as long. The 

 segments following gradually increase in length, becoming about as long as broad on 

 the fifth or sixth, and from half again to nearly twice as long as broad on the eighth or 

 ninth. The next three or four segments are similar, the length then very slowly de- 

 creasing, the segments in the middle of the cirri being about as long as broad and those 

 in the distal portion about twice as broad as long. The eighth, ninth, or tenth is a tran- 

 sition segment. Shortly after the transition segment the median portion of the distal 

 dorsal edge of the segments begins to become prominent. This very slowly increases 

 in height, arising from progressively more and more of the dorsal surface of the seg- 

 ments, which become progressively more and more carinate so that in the terminal 45 or 

 50 the dorsal surface is produced into a sharp, thin keel, straight in front, convex pos- 

 teriorly, the outer edge parallel with the median line of the cirrus, in height equal to 

 about one-third the lateral width of the segment which bears it. The opposing spine 

 is small and blunt, arising from the entire dorsal surface of the penultimate segment, 

 the apex subterminal or central, in height equal to about one third the diameter of the 

 penultimate segment. The terminal claw is small, about equal in length to the penulti- 

 mate segment, stout and moderately curved. The cirri are rounded in section in the 

 basal third, later becoming strongly compressed laterally and, when viewed from the 

 side, somewhat broader. 



The ends of the basal rays are visible as dorsoventrally elongated tubercles in the 

 angles of the calyx. Deep, though narrow, subradial clefts are present. 



The radials are very short, convex proximally and concave distally, with a small 

 sharp tubercle in the median portion of the proximal border. The IBn are about three 

 times as broad as long with the proximal border convex and the distal border concave, 

 in close lateral opposition and extending rather well up into the angles of the calyx; the 

 lateral edges are more or less denticulate, and there is a low, though sharp, serrate 



