A MONOGRAPH OF THE EXISTING CRENOIDS 163 



short spines or prominent tubercles, and their dorsal surface is thickly studded with 

 spines; they are sharply flattened laterally and are in close lateral apposition. 



Syzygies occur between brachials 3+4, again from between brachials 17+18 to 

 between brachials 19 + 20, and distally at intervals of from 4 to 9 muscular articulations. 



PI is 10 mm. long, enormously stout, tapering from the base to the tip, more rapidly 

 in the distal portion, and is composed of 20 segments. P 2 is 7 mm. long with 15 seg- 

 ments, much more slender than PI. The following pinnules are somewhat shorter, 

 but increase again distally to 14 mm. The distal pinnules have the first segment 

 short, broadly trapezoidal, the second trapezoidal but longer, the following to the 

 middle of the pinnule about as long as broad, and the remainder elongate. All the 

 pinnule segments have prominently everted spiny distal edges. 



Locality. Albatross station 4780; off Agattu Island, western Aleutians (lat. 

 5201'00" N., long. 17439'00" E.); 1,912 meters; bottom temperature 2.2 C.; gray 

 mud, sand, and pebbles; June 7, 1906 [A. H. Clark, 1907, 1908, 1909, 1912, 1918] 

 (5, U.S.N.M., 22630 [type], 35584, 36174). 



History. This species was described as Antedon villosa in 1907 from five specimens 

 that had been dredged by the Albatross at station 4780, at the western end of the Aleu- 

 tian Island chain, in the preceding year. In my revision of the genus Antedon published 

 later in 1907 Antedon villosa was made the type of the new genus Thalassometra. In 

 two papers published in 1908 Thalassometra villosa was said to belong to a group char- 

 acteristic of the oceanic area. In my revision of the family Thalassometridae published 

 in 1909 Thalassometra villosa was listed. In my memoir on the crinoids of the Indian 

 Ocean published in 1912 and in my report on the unstalked crinoids of the Siboga 

 expedition published in 1918 Thalassometra villosa was listed and the synonymy and 

 locality were given; hi the Siboga report villosa was included in the key to the species 

 of the genus Thalassometra. 



THALASSOMETRA ATTENUATA A. H. Clark 



PLATE 17, FIGURES 53, 54 

 [See also vol. 1, pt. 2, figs. 523, 524, 527, 528, p. 283.] 



Thalassometra attenuata A. H. CLARK, Proc. Biol. Soc. Washington, vol. 22, 1909, p. 147 (description; 

 2224' 00" N., 6651' 30" E.; 765 fathoms); Proc. U. S. Nat. Mus., vol. 39, 1911, p. 553 (com- 

 pared with Th. hirsuta); Crinoids of the Indian Ocean, 1912, p. 204 (synonymy; detailed 

 description; locality), fig. 38, p. 205; Smithsonian Misc. Coll., vol. 60, No. 15, 1913, p. 46 (com- 

 pared with Th. pergracilis [gracilis]); Unstalked crinoids of the Siboga-Exped., 1918, p. 168 (in 

 key; range), p. 171 (references); Journ. Linn. Soc. (Zool.), vol. 36, No. 249, April 1929, p. 654 (off 

 Mozambique; 500 fathoms). GISLEN, Kungl. Fysiogr. Sallsk. Handl., new ser., vol. 45, No. 11, 

 1934, p. 22. A. H. CLARK, John Murray Exped. 1933-34, Sci. Reports, vol. 4, No. 4, 1936 

 (Jan. 1, 1937), p. 87 (listed), p. 93 (Mabahiss station 143; notes; range), pp. 101, 104. 



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

 smooth dorsally, or bear a few low inconspicuous tubercles; the synarthrial tubercles 

 are rather prominent, but there is no median carination; and the cirri are arranged in 

 10 definite columns on the centrodorsal. The 10-13 arms are 80-120 mm. long, and 

 the cirri are 50 mm. long with 62-71 segments. 



Description. The centrodorsal is conical with the sides slightly convex, 3 mm. 

 broad at the base and 2 mm. high. The cirrus sockets are arranged in 10 columns 



