A MONOGRAPH OF THE EXISTING CRINOIDS 129 



that one of the specimens from station 170a bore the manuscript name Antedon vario- 

 spina. In my memoir on the unstalked crinoids of the Siboga expedition published hi 

 1918 breviradia was inserted in a key to the species of the genus Stiremetra, and the 

 references and range were given. 



STIREMETRA PERPLEXA (A. H. Clark) 



PLATE 14, FIGURE 44 



Thalassometra perpleia A. H. CLARK, Zool. Anz., vol. 39, No. 11/12, 1912, p. 426 (description; Siboga 



station 211). 

 Stiremelra perplexa A. H. CLARK, Unstalked crinoids of the Siboga-Exped., 1918, p. 161 (in key; 



range; references; detailed description; station 211), p. 274 (listed), pi. 23, fig. 63. 



Diagnostic features. The axillaries are shield-shaped, very long, half again as 

 long as broad, smooth, very sharply flattened laterally, the edges unmodified; the IBr) 

 have the central portion of the dorsal surface recumbent, making an angle of approxi- 

 mately 90 with the dorsoventral axis, the edges smooth and unmodified; the brachials 

 do not have overlapping spines; and the cirri are arranged in 10 definite columns on the 

 centrodorsal. The cirri are 35-40 mm. long with 62-66 segments, and there are 

 10 arms. 



Description. The centrodorsal is small, truncated conical, with the dorsal pole 

 entirely covered by elongate tubercles or papillae. The cirrus sockets are arranged in 

 10 closely crowded columns of 2 or 3 (usually 2) each. 



The cirri are XVIII, 62-66, from 35 to 40 mm. long. The longest cirrus segment, 

 usually the sixth, is from two and one-half to three times as long as broad. The seg- 

 ments following this slowly decrease in length, in the middle of the cirri being about as 

 long as broad, or slightly broader than long, and in the terminal fourth or fifth twice 

 as broad as long. The longer proximal segments have a slight median constriction and 

 slightly produced distal edges. The short distal segments have a prominent median 

 dorsal keel which, instead of being sharp along the crest, is broadly rounded. This keel 

 begins as a production of the distal dorsal border of the segment, but soon involves the 

 entire dorsal surface becoming, in profile view, rounded triangular, the apex near the 

 distal end, then evenly rounded, and in the terminal portion more or less straight 

 along the crest. 



The ends of the basal rays are concealed. 



The radials are concealed. The IBri are very narrow and bandlike, abutting directly 

 upon the centrodorsal though everywhere separated from it by narrow subradial clefts, 

 from 6 to 8 times as broad as long. They are everywhere of the same length, but while 

 the outer surface of their lateral portions is parallel to the axis of the IBr series, their 

 median portion is recumbent, making an angle of nearly 90 with that axis so that in 

 direct lateral view, that is, viewed at right angles to the dorsoventral axis, they are 

 only about one-third as long in the middorsal line as laterally. The IBr 2 (axillaries) 

 are rhombic with produced and broadly tuncated lateral angles, half again as long as 

 broad; the lateral edges are about as long as those of the IBrij the distal sides are 

 strongly concave; a posterior process, about as high as the anterior angle though some- 

 what broader and more rounded, incises the IBri ; the proximal two-thirds of the median 

 portion of the axillaries rises into a prominent, but well rounded, median elevation. 

 The elements of the IBr series are very sharply flattened against their neighbors, this 

 flattening persisting as far as the base of P t . 



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