188 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



edges produced and spinous and the distal angles produced, suggesting the conditions 

 seen in Oligometra serripinna. The pinnule, though stiff, is comparatively slender and 

 tapers evenly to the tip. P 3 is similar to P 2 but shorter, from 6 to 7 mm. long. P 4 is 

 4.5 mm. long. P 5 is similar to P 4 but shorter. The pinnules following are small and 

 weak. The slender distal pinnules are 9.5 mm. long. 



The color in alcohol is yellow, narrowly but frequently banded with purple, the 

 cirri purplish; or, purple and yellow in large blotches. 



Locality. Muscat, Arabia [A. H. Clark, 1912, 1913, 1918] (16, B. M.). 



History. This species was described by me in my memoir on the crinoids of the 

 Indian Ocean published in 1912, and was redescribed in a paper on the crinoids of the 

 British Museum published in 1913. It was included in the key to the species of 

 Decametra in my report on the crinoids of the Siboga expedition published in 1918. 



DECAMETHA MYLITTA A. H. Clark 



PLATE 22, FIGURE 110; PLATE 23, FIGURES 116, 117; PLATE 24, FIGURE 118 



IComatula laevissima GRUBE, Jahresb. schlesisch. Ges. vaterl. Cultur, 1875, p. 74 (description; 

 North Borneo). P. H. CARPENTER, Proc. Zool. Soc. London, 1882, 1883, p. 746 (correctly 

 referred by Bell to Antedon.) 



lAntedon laevissima BELL, Proc. Zool. Soc. London, 1882, p. 533 (listed). P. H. CARPENTER, Proc. 

 Zool. Soc. London, 1882, 1883, p. 746; Challenger Reports, Zoology, vol. 26, part 60, 1888, p. 54 

 (10-armed species), p. 193 (in key), p. 366 (bathymetrical range), p. 378 (Borneo). A. H. CLARK, 

 Crinoids of the Indian Ocean, 1912, p. 34 (of P. H. Carpenter, 1888 = Amphimetra milberti 

 [error]), p. 40 ( of Bell, 1902 = Amphimetra producta + A. molleri + Decametra taprobanes 

 + D. mobiusi), p. 289 (of Bell, 1902; account quoted); Smithsonian Misc. Coll., vol. 61, No. 15, 

 1913, p. 83 (of Bell, 1902 = Amphimetra flora + Decametra mobivsi + D. taprobanes; B. M., 

 MS. = Amphimetra producta). 



1 Amphimetra laevissima A. H. CLARK, Proc. Biol. Soc. Washington, vol. 22, 1909, p. 7 (listed); 

 Crinoids of the Indian Ocean, 1912, p. 112 (North Borneo). 



Dfcametra mylitta A. H. CLARK, Ann. Mag. Nat. Hist., ser. 8, vol. 10, 1912, p. 36 (description; 

 Siboga station 99); Unstalked crinoids of tbe Siboga-Exped., 1918, p. 117 (in key; range), p. 118 

 (detailed description; station 99; also Albatross station 5139), p. 272 (listed); pi. 20, fig. 50. 

 GISLEN, Vid. Medd. Dansk Naturh. Foren., vol. 83, 1927, p. 30 (no locality; notes). 



Diagnostic features. The cirri are 10-11 mm. long with 21-23 segments all of 

 which are markedly broader than long; P 2 is 9 mm. long with 17 segments, much longer 

 and stronger than the small and weak P! ; P 3 is about two-thirds as long as P 2 , which it 

 resembles, and is composed of 14 segments; the arms are 55-75 mm. long. 



Description. Tbe centrodorsal is discoidal with the flat dorsal pole 1.5 mm. in 

 diameter. The cirrus sockets are arranged in two closely crowded alternating rows. 



The cirri are XIX, 21-23, from 10 to 11 mm. long. The cirrus segments are sub- 

 equal in length, the first very short, the second slightly longer, the third and following 

 about twice as broad as long or slightly broader, the last three before the penultimate 

 increasing slightly in length so that the antepenultimate is about one-third again as 

 broad as long. The earlier segments have the dorsal surface swollen and truncated 

 distally so that the dorsal profile is serrate. After the first three the dorsal profile of 

 the individual segments becomes straighter, making a considerable angle with the 

 longitudinal axis of the cirrus, and the distal edge becomes straight, forming a very 

 finely spinous transverse ridge which, however, is not raised above the general dorsal 

 surface of the segment. This transverse ridge becomes gradually more and more 

 marked, at the same time moving more and more toward the center of the dorsal sur- 



