132 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



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

 the Indian Ocean published in 1912. I said that it appears to be a very distinct species. 

 The large cirri with numerous segments resemble those of Daidalometra arachnoides, 

 but the centrodorsal is very much larger and the columns of cirrus sockets are segre- 

 gated into widely separated pairs instead of being closely crowded. The ossicles of the 

 calyx and arm bases also lack the spinous edges and the high median carinate processes 

 so characteristic of that form. The small centrodorsal of S. spinicirra, which is hemi- 

 spherical or bluntly conical with no differentiation into areas, as well as the short cirri 

 with few segments, each of which bears a spine, serves to differentiate that species. 

 Stiremetm acutiradia also has a small centrodorsal with only about 15 cirrus sockets 

 which are differently arranged. Stiremetra breviradia has cirri with 40-50 segments, 

 "or a few more," but the centrodorsal is of the type found in D. arachnoides, quite 

 different from that in the species under consideration. It is probable, however, that 

 this is the species to which S. carinifera is most closely allied. 



In my memoir on the unstalked crinoids of the Siboga expedition published in 1918 

 carinifera was inserted in the key to the species of Stiremetra and the original reference 

 was given. 



STIREMETRA ACUTIRADIA (P. H. Carpenter) 



Antedon acutiradia P. H. CARPENTER, Quart. Journ. Micr. Sci., vol. 27, 1887, pp. 386, 387 (sacculi 

 present between the side plates; nomen nudum); Challenger Reports, Zool., vol. 26, pt. 60, 1888, 

 p. 113 (description; Challenger station 175), pi. 11, figs. 3, 4. HARTLAUB, Bull. Mus. Comp. 

 Zool., vol. 27, No. 4, 1895, p. 131 (systematic and bathymetrical relationships). HAMANN, 

 Bronn's Klassen und Ordnungen des Tier-Reichs, vol. 2, Abt. 3, 1907, p. 1578 (listed). A. H. 

 CLARK, Crinoids of the Indian Ocean, 1912, p. 33 (of P. H. Carpenter, 1888= Stiremetra acutiradia). 



Thalassometra acutiradia A. H. CLARK, Smithsonian Misc. Coll., vol. 50, pt. 3, 1907, p. 300 (listed). 



Stiremetra aculiradia A. H. CLARK, Proc. Biol. Soc. Washington, vol. 22, 1909, p. 15 (listed); Crinoids 

 of the Indian Ocean, 1912, p. 33 (identity), p. 211 (synonymy; locality); Smithsonian Misc. 

 Coll., vol. 61, No. 15, 1913, p. 45 (published references to specimens in the B. M.; Challenger 

 Station 175); Unstalked crinoids of the Siboga-'Exped., 1918, p. 161 (in key; range; references). 



Diagnostic features. The axillaries are long, longer than broad ; the IBr series and 

 proximal brachials have a smooth dorsal surface, straight sharp edges, and a sharp 

 median keel ; the first four brachials do not bear dorsal spines ; and the cirri are arranged 

 in 10 definite columns on the centrodorsal. The 10 arms are probably about 50 mm. 

 long. 



Description. The centrodorsal is a somewhat elongated hemisphere with a 

 papillose dorsal pole. According to the figure the cirrus sockets are arranged in a 

 single rather crowded marginal row, two sockets in each radial area; the radial areas 

 are not specially differentiated. 



The cirri, according to the description, are about XV; the fourth and some of the 

 following segments are much longer than broad with traces of dorsal spines. 



The raclials are just visible beyond the rim of the centrodorsal. The IBri are 

 partly free laterally and are deeply incised by the sharp proximal angles of the IBr 2 

 (axillaries), which are longer than broad. Both ossicles are very sharply convex and 

 almost carinate, but the IBr 2 are broader and have a more rounded surface than the 

 IBr 1; which are partly hidden beneath their lateral angles. The elements of the IBr 

 series and first brachials have straight edges and flattened sides. The inner side of the 

 second brachial and the hypozygal of the first syzygial pair are also flattened. 



