270 BULLETIN 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



Diagnosis. A genus of Thysanometrinae in which the radial facets are oblong, 

 broader than long, the muscular fossae large, transversely rounded-oblong, separated 

 from the interarticular ligament fossae by horizontal ridges, the exterior ends of which 

 are more or less curved downwards; the centrodorsal is hemispherical as a rule, but 

 varies from conical to discoidal ; the distal pinnules tend to be longer than the proximal 

 ones. 



Type species.- -Antedon tenelloides A. H. Clark, 1907. 



Geographical range. Known from southern Japan to the Philippines, Kei, and 

 Admiralty Islands. 



Bathymetrical range. From 128 to 548 meters. 



KEY TO THE SPECIES OF THYSANOMETRA 



a 1 . Brachials following the second syzygy wedge-shaped, twice as broad as long, soon becoming oblong, 

 much broader than long; PI nearly half again as long as P 2 ; 15-17 cirrus segments (south- 

 ern Japan; 128-360 meters) tenelloides (p. 270) 



a 2 . Brachials beyond the second syzygy triangular, as long as broad, in the outer part of the arm 

 becoming very obliquely wedge-shaped and longer than broad; PI about the same length as 

 P 2 , or shorter, 15-25+ cirrus segments (north of the Admiralty Islands, Philippines; 225-548 

 meters) tenuicirra (p. 272) 



THYSANOMETRA TENELLOIDES (A. H. Clark) 



[See vol. 1, pt. 1, figs. 285 (p. 261), 372 (p. 299), 498 (p. 369) ; pt. 2, figs. 89-90 (p. 62), 282 (p. 215), 



752 (p. 349)] 

 Antedon tenelloides A. H. CLARK, Proc. U.S. Nat. Mus., vol. 33, 1907, p. 73 (description; Albatross 



Sta. 5092). 

 Thysanometra tenelloides A. H. CLARK, Smithsonian Misc. Coll., vol. 50, pt. 3, 1907, p. 351 (listed); 



Proc. U.S. Nat. Mus., vol. 34, 1908, p. 319 (Japan); Crinoids of the Indian Ocean, 1912, p. 



244 (synonymy; southern Japan, 70 fms.) ; Smithsonian Misc. Coll., vol. 61, No. 15, 1913, p. 



64 (comparison with Th. tenuicirra) Journ. Washington Acad. Sci., vol. 5, No. 6, 1915, p. 



215 (southern Japanese species; range and its significance); Unstalked crinoids of the Siboga- 



Exped. 1918, p. 218 (in key; range; references). 



Diagnostic features . The brachials following the second syzygy are wedge-shaped, 

 twice as broad as long, soon becoming oblong, much broader than long; when the arms 

 are 110 mm. long, the cirri are LX-LXX, 15-17, 35 mm. long. P, is 14 mm. long with 

 35 to 40 short segments and P 2 is 10 mm. long with 20 segments of which all but the 

 basal 3 or 4 are much elongated. 



Description. The centrodorsal is low hemispherical or more or less discoidal, 

 always with a large bare polar area with a more or less pronounced tubercle in the 

 center surrounded by numerous shallow pits. The cirrus sockets are very numerous 

 and closely crowded, irregular in position, but arranged roughly in about three rows. 



The cirri are LX-LXX, 15-17 (usually 15-16), 35 mm. long, from one quarter to 

 one third the length of the arms, slender, strongly compressed laterally, with no trace 

 of dorsal processes. The first segment is about as long as broad, the second is about 

 twice as long as broad, with its ends somewhat enlarged, the third is about three times 

 as long as broad, practically oblong, and the fourth is intermediate between the third 

 and the fifth, which is about four times as long as broad. The segments immediately 

 following resemble the fifth; after the eighth or ninth they gradually become propor- 

 tionately shorter, the third from the tip being about three times as long as broad; the 

 two terminal segments are of about the same proportions, but decrease slightly in 

 breadth. The terminal claw is slender and almost straight, about half the length of 

 the penultimate segment. 



