236 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



OLIGOMETRA SERRIPINNA var. IMBRICATA A. H. Clark 



PLATE 28, FIGURES 145-147 

 [See also vol. 1, pt. 2, figs. 492, 493 (pinnule tip), p. 273.] 



Oligometra imbricata A. H. CLARK, Proc. Biol. Soc. Washington, vol. 21, 1908, p. 228 (description. 

 ?Tranquebar) ; vol. 22, 1909, p. 7 (listed), p. 42 (compared with 0. [Decametra] studeri) Vid; 

 Medd. Naturh. Foren. K0benhavn, 1909, p. 180 (?Tranquebar; includes cupuliferus, var., 

 compared with serripinna) ; Crinoids of the Indian Ocean, 1912, p. 168 (synonymy; Ganjam 

 coast, 24-30 fms.; ?India; also ?Tranquebar) , fig. 27, p. 170; Unstalked crinoids of the Siboga- 

 Exped., 1918, p. 129 (in key; range). 



Antedon cupuliferus, var. (Liitken, MS.) A. H. CLARK, Vid. Medd. Naturh. Foren. K0benhavn; 

 1909, p. 117 (synonym of 0. imbricata). 



Diagnostic features.- The distal ends of the brachials in the proximal third of the 

 arm are much produced and are turned abruptly outward; the segments of P 2 usually 

 have slightly developed lateral processes. 



Description. The centrodorsal is rather large, discoidal, with a large concave 

 polar area. The cirrus sockets are arranged in a single marginal row. 



The cirri are XVI-XVII, 23-28 (usually 24-26), about 12 mm. long. All of the 

 segments except the terminal 5 or 6, which are about as long as broad, are broader 

 than long, the basal very much so. The segments are flattened dorsally; basally 

 they have prominent distal dorsal ends which show a tendency to rise into a low 

 transverse ridge which in the outer part of the cirri becomes more distinct and grad- 

 ually narrower, at the same tune gaining hi height so that the terminal 6 or 7 seg- 

 ments have minute median dorsal spines. The opposing spine is prominent, but 

 slender, in length not reaching quite the width of the penultimate segment. The 

 terminal claw is longer than the penultimate segment, strongly curved basally but 

 becoming nearly straight distally. 



The distal ends of the radials are even with the rim of the centrodorsal. The 

 IBr series and brachials have about the same proportions as those of 0. serripinna, 

 and the synarthrial tubercles are about as prominent as in that species. The brachials 

 differ, however, ha having very strongly produced and overlapping distal edges. 



The arms are about 45 mm. long. 



P 2 is much longer and stouter than P]. The following pinnules decrease rapidly 

 in size, remain uniform for some time, then slowly increase distally. The basal seg- 

 ments of the lower pinnules may be more or less carinate, and the distal segments 

 expand somewhat from the proximal to the distal end, giving the edge of the pinnules 

 a serrated outline. 



The color in alcohol is grayish brown, the perisome darker. 



Remarks. Although the strongly produced distal ends of the brachials hi the 

 earlier portion of the arms give this form a very distinctive appearance, it is probably 

 only a variety of 0. serripinna. Oligometra serripinna occurs on the Ganjam coast 

 and at Ceylon, and individuals from various parts of its range sometimes show, more 

 or less developed, the feature characteristic of imbricata. 



Notes. In 1909 I wrote that in the original description of this species I had 

 confined myself to an exposition of only the most essential characters, as the subjection 

 of the two specimens to a more detailed examination would involve a very considerable 

 risk owing to their poor state of preservation. 



