158 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



long axis as the pinnule; on the fourth and fifth segments its crest may he indented so 

 that it has two peaks. The outer prominence is not so long or so high; it arises from 

 the distal third of the dorsolateral edge; its summit is rough with spines. The dorsal 

 surface between the prominences is flat so that the general appearance of the dorsal 

 surface of the proximal part of the pinnule is that of a flat-bottomed channel running 

 between long and high prominences on the inner side and short and lower prominences 

 on the outer. Between the sixth and ninth segments the long inner prominence de- 

 creases and becomes obliquely inclined to the dorsal surface, and finally passes into a 

 lateral extension of it. At the same time the outer prominence rapidly decreases, to 

 disappear at about the twelfth segment. The distal segments of the pinnule, as viewed 

 from above, are broad and flat, considerably broader than long, and broader distally 

 than proximally, the greater distal width being on the inner side. 



The disk is very heavily plated. 



Locality.— Northwest of Sokotra (lat. 14°20' N., long. 52°30' E.); 2,194 meters 

 (1,200 fathoms); Capt. V. F. Sparks, cable repair ship Electra, July 1909 [A. H. Clark, 

 1911, 1912, 1913, 1937; John, 1937] (1, B. M.). 



History.- — During a visit to the British Museum in 1910 I found this species in a 

 jar with new species of Pachylometra (Perissometra) and Thaumatometra, and recorded 

 it as a new species of Thalassometra in 1911, 1912, 1913, and 1937. It was formally 

 described by D. Dilwyn Jolm in 1937. 



THALASSOMETRA AGASSIZn (Harllaub) 



[See vol. 1, pt. 2, pi. 3, figs. 981-983, pi. 13, fig. 1050, pi. 14, fig. 1059, pi. 22, fig. 1140, pi. 27, figs. 



1171, 1172.] 



Antedon agassizii IIartlaub, Bull. Mus. Comp. Zool., vol. 27, No. 4, 1895, pp. 129, 131 (description 

 and detailed discussion; Albatross stations 3357, 3408, 3409), pi. 1, figs. 4, 7, 8, pi. 2, figs. 16, 18, 

 19, pi. 3, fig. 23, pi. 4, fig. 26.— H. L. Claiuc, Proc. Washington Acad. Sci., vol. 4, 1902, p. 522 — 

 Hamann, Bronn's Klassen und Ordnungen des Tier-Reichs, vol. 2, Abt. 3, 1907, pp. 1578, 1580 

 (listed). 



Thalassometra agassizi A. H. Clark, Smithsonian Misc. Coll., vol. 50, pt. 3, 1907, p. 360 (listed); 

 Proc. Biol. Soc. Washington, vol. 22, 1909, p. 14 (listed). 



Thalassometra agassizii A. H. Clark, Crinoids of the Indian Ocean, 1912, p. 203 (synonymy; locality); 

 Unstalked crinoids of the <Sj'6offa-Exped., 1918, p. 167 (in key; range), p. 170 (references). 



Diagnostic features. — The elements of the division series and lower brachials are 

 bordered proximally and distally with coarse blunt spines, with occasionally a few on 

 (lie dorsal surface; and the cirri are arranged in 10 columns on the centrodorsal, each 

 radial pair of columns with an additional cirrus between them near the rim of the 

 centrodorsal. The 10-12 arms are about 175 mm. long, and the cirri are about 40 

 mm. long with 60+ segments. 



Description. — The centrodorsal is of moderate size, dome-shaped with a bare dorsal 

 pole which is beset with small spines. The cirrus sockets are arranged in three columns 

 in each radial area, the two outer columns, which meet distally, of three, sometimes 

 two, sockets, the central of one. The radial areas are separated by slight Lnterradial 

 ridges. 



The cirri are XV-XX1J, with up to 60+ segments, about 40 mm. long. They are 

 slender, and in the outer half strongly compressed laterally. The first two segments 

 air short, the third is longer, the fourth is about as long as the third, and the sixth is 



