A MONOGRAPH OF THE EXISTING CRINOIDS 183 



Thalassometra multispina (part) A. H. CLARK, Smithsonian Misc. Coll., vol. 61, No. 15, 1913, p. 47 

 (Challenger station 135 [but not station 344= Th. multispina}). GISLN, Ark. Zool., vol. 19A, 

 No. 32, 1928, p. 24 (young specimen mentioned, but not pentacrinoids Xos. 1-3). 



Thalassometra setosa A. II. CLARK, The Danish Ingolf-Exped., vol. 4, Xo. 5, Crinoidea, 1923, p. 40 

 (range), p. 57 (in key). 



Diagnostic features. The cirri are arranged in 15 crowded columns on the centro- 

 dorsal; the elements of the division series and lower brachials have a few scattered fine 

 spines on the dorsal surface. There are 13 arms probably about 50 mm. long, and the 

 cirri have 35 segments. 



Characters. The centrodorsal is flattened-hemispherical with the cirri apparently 

 irregularly arranged, possibly in 15 columns, or 3 columns in each radial area. 



The cirri are about XXXII, in general similar to those of Th. multispina, but they 

 may have as many as 35 segments. 



The radials are visible. The IBr series, brachials, and pinnule segments are less 

 distinctly spinous than those of Th. multispina. 



There are 13 arms, two IIBr 4(3+4) series and one IIBr 2 series being present. 

 On the arms arising from the IIBr 2 series the first syzygy is between brachials 3+4; 

 but in the arms following the two IIBr 4(3+4) series one has the first syzygy between 

 brachials 1+2, while in the other it is between bracbials 3+4. 



PI has somewhat the same flattened appearance on the outer side as is traceable in 

 Th. multispina, but it is so slight as to be hardly recognizable except by a trained eye, 

 and the same may be said of the lateral flattening of the lower brachials. 



The plating of the disk is very incomplete, and the ambulacral skeleton of the pin- 

 nules is by no means well differentiated. 



The characters given above are taken from Carpenter's notes on the only known 

 specimen, supplemented by his figure and Gislen's statement of the number of the cirri. 



Locality. Challenger station 135G; south Atlantic, off Tristan da Cunha (lat. 

 3710'50" S., long. 1218'30" W.); 1,005 meters; hard ground; October 18, 1873 

 [Wyville Thomson, 1877; P. H. Carpenter, 1888; A. H. Clark, 1913, 1923; Gislen, 

 1928] (1, B. M.). 



History. This species was first mentioned in 1877 by Prof. Sir Wyville Thomson 

 who noted that the Challenger dredged Antedon, sp., off Tristan da Cunha in 550 fathoms. 



In the introductory chapter on geographical and bathymetrical distribution in the 

 Challenger report on the comatulids published in 1888 Dr. P. H. Carpenter mentioned 

 "Antedon setosa from off Tristan da Cunha" (p. 34), but in the descriptive portion of 

 the work he included the single mutilated specimen from station 135G under Antedon 

 multispina in his supplementary account of that species (p. 248) as a member of the 

 Granulifera group. He gave a number of features by which the specimen from Tristan 

 da Cunha is distinguished from the four dredged near Ascension (=Th. multispina), 

 and figured it. 



In my earlier papers this form was included in Thalassometra multispina, and I did 

 not distinguish the two in my notes on the crinoids of the British Museum published 

 in 1913. In my report on the crinoids of the Ingolf expedition published in 1923 setosa 

 was included in the key to the species of Thalassometra occurring in the Atlantic, and 

 the locality and depth were given. In 1928 Prof. Torsten Gislen noted that the speci- 

 men of Thalassometra multispina from Challenger station 135G had the cirri about 

 XXXII. 



