A MONOGRAPH OF THE EXISTING CKINOIDS 113 



Soc. Washington, vol. 29, 1916, pp. 106, 108 'vol.|^31, 1918, p. 37; Unstalked crinoids of the 

 Siboga-Exped., 1918, p. 125. 



Diagnosis. — A genus of Colobometridae including small species with 10 arms 

 30-60 mm. long; Pi, Po, and Pa are similar and of the same length, still and spincUke, 

 composed of 11-16 segments which have everted and spinous distal ends; the 14-21 

 cirrus segments are mostly about as long as broad. 



Geographical range. — From southern Japan to the Philippine Islands. 



Baihymetrical range. — From 100 to 106 meters. 



History. — The first known species of this genus was mistaken by me for Hartlaub's 

 Antedon japonica and was recorded as Oligometra japonica in 1908. The second species 

 was recorded as Oligometra japonica in 1911. In 1912 the first species was named 

 Colobometra (Prometra) owstoni, and in 1915 it was mentioned as Prometra owstoni. 

 The second species was described as Prometra longipinna in 1916. Since 1916 both 

 species have remained in the genus Prometra. 



KEY TO THE SPECIES IN THE GENUS ALISOMETRA 



a'. Cirrus segments 16-21 (usually 18 or 19); P1-P3 with 14-16 segments; arms 55-60 mm. long 

 (southern Japan ; 100 meters) owstoni (p. 113) 



a'. Cirrus segments 14-15; Pi-Pj with 11 or 12 segments; arms about 30 mm. long (Philippine Islands; 

 106 meters) longipinna (p. 115) 



AUSOMETRA OWSTONI (A. H. aark) 



Plate 13, Figures 65, 66 



[See also vol. 1, pt. 1, fig. 351 (cirrus), p. 291; pt. 2, fig. 299 (proximal pinnules), p. 221; fig. 327 

 (middle pinnules), p. 227; fig. 348 (distal pinnules), p. 229.] 



Oligometra japonica A. H. Clark, Proc. U. S. Nat. Mus., vol. 34, 1908, p. 308 (Sagami Bay, 55 fms. ; 



notes); Proc. Biol. Soc. Washington, vol. 22, 1909, p. 42 (compeared with O. slvderi); Crinoids 



of the Indian Ocean, 1912, p. 175 (in part; same record). 

 Colobomelra (Prometra) owstoni A. H. Clark, Crinoids of the Indian Ocean, 1912, p. 322 (new name 



for Oligometra japonica A. H. Clark, 1908, not of Hartlaub, 1890; compared with C. [P.] brevi- 



cirra; characters; discussion). 

 Prometra oxostoni A. H. Clark, Journ. Washington Acad. Sci., vol. 5, No. 6, 1915, p. 214 (nomen 



nudum; southern Japanese species; range and its significance); Proc. Biol. Soc. Washington, 



vol. 29, 1916, p. 106 (description; Sagami Bay, 55 fms.) ; Unstalked crinoids of the Siboga-Exped., 



1918, p. 125 (in key; range). 



Diagnostic features. — The cirri have 16-21 (usually 18 or 19) segments and are 

 10 mm. long; Pj, P2, and P3 have 14-16 segments and are 8 mm. long; the arms are 

 55-60 mm. long. 



Description.- — The centrodorsal is discoidal, rather thick, vnth the broad flat 

 polar area 2 mm. in diameter and covered with nvmicrous small imiform rounded 

 tubercles. The cirri are arranged in 2 irregular alternating marginal rows. 



The cu-ri are XXVII, 16-21 (usually 18-19), 10 mm. long. The first segment is 

 short, much broader than long, and those follo\\nng gradually increase in length to the 

 fourth or seventh (usually fifth or sixth) which, with the remainder, is about as long as 

 broad. On the second or third segment the median portion of the distal dorsal edge 

 becomes produced, this production on the 2 or 3 following involving the entire distal 

 dorsal edge so that, viewed dorsally, it appeai-s as a crescentic ridge with a serrate 

 apex, the horns of the crescent touching the distal dorsal angles of the segments. 



