164 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



of usually 2 each, the radial pairs of columns being usually slightly separated in the 

 midradial line by a shallow furrow or a coarsely tubercular ridge. 



The cirri are XX, 62-71, 50 mm. long, elongated and very slender. The longest 

 proximal segments are twice as long as broad or slightly longer, and the twenty-fifth 

 and following are slightly broader than long. The segments after the seventeenth- 

 twentieth have the distal dorsal edge produced into a serrate ridge that soon gives 

 place to small carinate dorsal spines. 



The ends of the basal rays are visible as small, though rather prominent, tubercles 

 hi the interradial angles. 



The radials are entirely concealed by the centrodorsal, or are just visible beyond 

 its run, sometimes bearing on the dorsal surface a row of small tubercles. The IBri 

 are very short, widely chevron-shaped, with the proximal edge and the lateral thirds 

 of the distal edge somewhat everted, and the distal lateral angles more or less produced. 

 The IBr 2 (axillaries) are triangular, twice as broad as long with the anterior edges 

 somewhat everted and the lateral angles more or less produced. The IIBr series, 

 when present, are 4(3+4); they are developed in two of the six specimens hi the type 

 series. The elements of the IBr series and first two brachials are smooth dorsally or 

 bear a few low inconspicuous tubercles ; then- lateral borders are usually slightly spinous ; 

 the synarthrial tubercles are rather prominent. The lateral edges of the elements of 

 the IIBr series are more or less produced. 



The 10-13 arms are from 80 to 90 mm. long. They are exceedingly slender, hav- 

 ing in general more the appearance of the arms of some slender antedonid than of those 

 of a thalassometrid. The first brachials are short, wedge-shaped, twice as long ex- 

 teriorly as ulteriorly, basally united ulteriorly, with the anterior and posterior edges 

 slightly thickened, the lateral edges somewhat produced, and the anterolateral angles, 

 both interior and exterior, more or less produced. The second brachials are similar in 

 size and shape. The first syzygial pah- (composed of brachials 3 + 4) is usually slightly 

 longer ulteriorly than exteriorly, from half again to about as broad as long. The next 

 three or four brachials are approximately oblong, twice as broad as long, and those 

 following become triangular, as long as broad, distally slowly increasing hi length and 

 becoming wedge-shaped, being twice as long as broad in the outer part of the arms. 

 The brachials beyond the second have the dorsal surface studded with very fine short 

 spines or sharp tubercles which hi some individuals are nearly obsolete. At about the 

 end of the proximal fourth of the arm the brachials begin to develop prominent longi- 

 tudinal striations which increase in frequency and in height distally. The proximal 

 oblong brachials have the proximal and distal ends somewhat prominent. After about 

 the twentieth brachial the distal edges begin to overlap, and in the distal portion of the 

 arms the brachials have the distal part somewhat expanded and the central part some- 

 what constricted so that the outer portions of the arms closely resemble those of the 

 species of Antedonidae. 



The pinnules are essentially as hi the related species; the three lowest pinnules on 

 either side of the arm are very strongly carinate. 



The color hi alcohol is white, the perisome, and sometimes the IBr series and arm 

 bases, light brownish. 



Notes. The arms of the specimen from Mabahiss station 143 were probably about 

 120 mm. long. The cirri are about 45 mm. long and consist of 55 segments of which 



