A MONOGRAPH OF THE EXISTING CRINOIDS 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 Colobomctridae including small species with 10 arms 

 30-60 mm. long; PI, P 2 , and P 3 are similar and of the same length, stiff and spinclike, 

 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. 



Bathymetrifal range. From 100 to 106 rasters. 



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

 Antedon japonica and was recorded as Oligometrajaponica 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 1 . Cirrus segments 16-21 (usually 18 or 19); Pi-Pj with 14-16 segments; arms 55-60 mm. long 

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



a 2 . Cirrus segments 14-15; Pr-P 3 with 11 or 12 segments; arms about 30 mm. long (Philippine Islands; 

 106 meters) longipinna (p. 115) 



ALISOMETRA OWSTONI (A. H. Clark) 



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.] 



Oligometrajaponica 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 (compared with 0. sluderi) ; Crinoids 



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

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



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



cirra; characters; discussion). 

 Promelra owstoni 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; PI, P 2 , and P 3 have 14-16 segments and are 8 mm. long; the arms are 

 55-60 mm. long. 



Description. The centrodorsal is discoidal, rather thick, with the broad flat 

 polar area 2 mm. in diameter and covered with numerous small uniform rounded 

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



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

 short, much broader than long, and those following 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 appears as a cresccntic ridge with a serrate 

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



