832 BULLETIN 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



The basals are very short, with the interradial portion swollen and rising to the 

 height of the ridge on the proximal portion of the centrodorsal, and the radial portions 

 reduced to a narrow line separating the radial from the centrodorsal. 



The radials are short, 4 or 5 tunes as broad as long in the median line. 



The IBri are approximately oblong, nearly twice as broad as long in the median 

 line; the median portion of the distal edge is slightly incised. The IBr 2 (axillaries) 

 are nearly rhombic, about as broad as long, with the anterior angle slightly produced. 

 The proximal portion of the lateral edge may be produced into a rather prominent 

 tubercle corresponding to a slight thickening of the anterolateral angle of the IBr 1( 

 or both the lateral edge of the IBr, and that of the axillary may be cut away so that 

 they form an obtuse angle with each other as in A. conifer. 



None of the 10 arms are preserved beyond the ninth brachial (the hypozygal of the 

 third syzygial pair). The brachials resemble those of A. balanoides, but are propor- 

 tionately slightly shorter. 



The length of the type specimen from the tip of the centrodorsal to the third 

 syzygy is 13 mm. 



NOTES [BY A.M.C].- -In 1924 Gislen gave some details and figures of the brachial 

 articulations of this species, presumably from a study of the Thor specimen, and in 1927 

 Mortensen published a figure of the calyx and arm bases, again probably of this speci- 

 men. It appears from this that the cirrus sockets are not in very regular columns. 

 He did not give the size of the centrodorsal but the specimen is presumably larger than 

 the type since the basals are only visible as small interradial triangles. Even in the 

 type with the centrodorsal about 2.5 mm. high the radial parts of the basals are "reduced 

 to a narrow line separating the radial from the centrodorsal." In A. balanoides from the 

 West Indies the basals seem to be a little more prominent since the holotype from Blake 

 station 151, with the centrodorsal probably about 4 mm. high, still has the basals 

 forming a continuous band around the calyx. However, there must be considerable 

 variation in this since the Challenger specimen of balanoides, which also has the cen- 

 trodorsal 4 mm. high, has the basals barely visible radially. 



Localities. Helga station CXX; northwest of Galway Bay, western Ireland Qat. 

 5358' N., long. 1224' W.); 698 meters; August 24, 1901 [A. H. Clark, 1912, 1918, 

 1923] (1, U.S.N.M., 35779). Type locality. 



Thor; southwest of the Faroe Islands Gat. 6115' N., long. 935' W.); 900 meters; 

 May 22, 1904 [A. H. Clark, 1923; Gislen, 1924; Mortensen, 1927] (1, C.M.). 



SIBOGACRINUS, gen. nov., A. H. Clark 



Atelecrinus (part) A. H. CLARK, Notes Leyden Mus., vol. 34, 1912, p. 153; Unstalked crinoids of 

 the Si&offa-Exped., 1918, pp. viii, 266, 269. 



Diagnosis. A genus of Atelecrinidae in which the arms are 10 in number, IBr 

 series being present with the IBr 2 axillary, and the first syzygy is between brachials 

 3+4. The basals are very large, their height equal to more than half their width, 

 and are broadly in contact laterally. The surface of the centrodorsal is smooth, with 

 no elevations flanking the cirrus sockets. The cirri are recurved, with not more than 

 20 segments, of which those in the outer third are much shorter than the proximal, 

 and but little longer than broad. The terminal claw is long, stout, and recurved. 



Type species. Atelecrinus anomalus A. H. Clark, 1912. 



Geographical range. Only known from the Moluccas. 



Bathymetrical range. Only known from 1633 meters. 



