PAKT 6 A MONOGRAPH OF THE EXISTING CRINOIDS 755 



broader than long, the second wedge-shaped, longer than broad, and the following 

 becoming progressively elongated. 



Locality. Western Aleutian Islands; Koniuji Island bearing S. 2230' W., 27 

 miles distant (lat. 5238'00" N., long. 17449'00" W.) ; 3229 meters; May 31, 1906 [A. H. 

 Clark, 1908] (1, U.S.N.M., 22672). 



THAUMATOMETRA THYSBE A. H. Clark 



Thaumalometra thysbe A. H. CLARK, Notes Leyden Mus., vol. 34, 1912, p. 149 (description; Siboga 

 sta. 52); Unstalked crinoids of the Siboga-Exped., 1918, p. 255 (in key; range), p. 257 (detailed 

 description; sta. 52), p. 271 (listed), pi. 26, fig. 98. 



Diagnostic features. The cirri are XL-LX, the longest with 13 to 16 segments, of 

 which the maximum length is from three to six times the median width; the ante- 

 penultimate is not more than twice as long as broad and the penultimate is only a little 

 longer than broad; Pj has over 15 segments. When the arms are 30 mm. long, the cirri 

 are about 9 mm. [NOTE BY A.M.C. In the key given in the Siboga report, Mr. Clark 

 included thysbe in the section with the third and fourth cirrus segments from the end at 

 least twice as long as wide although in his description of the type of thysbe he writes 

 that the two segments before the penultimate are only a third to a half again as long 

 as wide. I have altered the position of thysbe in the present key accordingly.] 



Description. The centrodorsal is small and rounded conical in shape. 



The cirri are about XL, 15-16, 9 mm. long. The first segment is short, the second 

 about as long as the diameter of the expanded distal end, the third twice as long its distal 

 diameter and the fourth slightly longer [presumably about three times as long as its 

 median diameter A.M.C.]. The following segments gradually decrease in length so 

 that the last two before the penultimate are from a third to a half again as long as 

 broad. The earlier segments have greatly enlarged ends, the distal end being much 

 expanded and overlapping the base of the succeeding segment; as the segments become 

 shorter, the dorsal and ventral profiles become straighter and the egments become com- 

 pressed laterally so that they appear broader in lateral view; on the distal short segments 

 the median portion of the distal edge on the dorsal side projects slightly over the base of 

 the following segment. 



The radials are just visible in the median line beyond the edge of the centrodorsal, but 

 extend well out in the interradial angles; their distal angles are slightly separated so that 

 the bases of the IBri are not quite in apposition. 



The IBri are very short, almost oblong, about four times as broad as the exterior 

 length, which is slightly greater than the median length; the lateral borders of adjacent 

 IBr! make an angle of about 90 with each other; the distal edges are narrowly everted 

 and very finely spinous. The IBr 2 (axillaries) are about as broad as long; the distal 

 edges make appro ximately a right angle with each other; the distal angle is not produced; 

 a broad proximal angle incises the IBri ; the lateral angles extend considerably beyond 

 the distal angles of the IBr! ; the distal edges are evenly and very finely spinous. 



The 10 arms are 30 mm. long, resembling those of the other species of the genus. 

 The distal edges of the brachials are moderately everted and finely spinous. 



Syzygies occur between brachials 3+4, 9 + 10, 14 + 15, and distally at intervals of 

 two muscular articulations. 



P! is excessively delicate, about 6.5 mm. long, composed of somewhat more than 

 15 segments, of which the first is very short, the second is longer, the third is about as 



556-622 67 49 



