746 BULLETIX 82, UNITED STATES NATIONAL MUSEUM VOLUME 1 



(composed of the third aud fourth brachials) is not quite so long as broad. The 

 following brachials are slightly wedge-shaped, not quite so long as broad, after about 

 the sixteenth becoming triangular, not quite so long as broad, and after the middle of 

 the arm gradually becoming wedge-shaped again and then elongate, the terminal 

 brachials being about twice as long as broad or even longer. Beginning with the 

 second brachial, strong articular tubercles are developed; in some individuals these 

 are much more conspicuous than in others, and in small specimens they may even be 

 wanting. These die away after the tenth brachial and the arms become smooth 

 until the outer half (or two-thirds in the smaller individuals) when the articulations 

 begin to become prominent, the brachials distally becoming markedly constricted 

 centrally. 



Syzygies occur between brachials 3 + 4, 9 + 10, and 14+15, and distally at intervals 

 of 2 or 3 muscular articulations. 



P, is 20 mm. long, composed of 35 segments, of which the first four or five are 

 about as long as broad with the corners cut away and the following become progressively 

 elongated. P2 is 18 mm. long, with 20 segments, of which the first two are about as 

 long as broad, the next two are longer than broad, and the remainder, which are 

 more slender, rapidly become elongated. P2 basaUy is about as stout as Pi, but it 

 tapers less rapidly and therefore appears somewhat stouter with more elongate seg- 

 ments, though the portion extending beyond the large gonad which it bears is slender 

 and filiform hke the distal portion of Pi. The following pinnules to P7 or Pg are similar 

 and of the same length. The remaining pinnules have no gonad and become more 

 slender and more elongate. The distal pinnules are 21 mm. long, with the first seg- 

 ment short and broad, the second longer than broad and trapezoidal, and the 

 remainder much elongated with swollen articulations. 



Notes. — Gislen (1927) has described under the name Thaumatometra cf. knuis a 

 specimen collected by Dr. Mortensen in the Sagami Sea, which is small compared with 

 the other loiown specimens of tenuis, having the arm length only 40 mm. It has also 

 lost all the cirri, thus rendering certain identification difficult. 



The centrodorsal is subconical, 1.7 mm. in diameter and 1.0 mm. in height. 

 There are about XLV cirrus sockets arranged in three or four close alternating whorls, 

 leaving free a low smooth dorsal cone 0.5 mm. in diameter. 



The radials protrude slightly at the corners. The IBri are four times as broad 

 as long and are incised by the stout backward prolongation of the IBr2 (a.xillaries). 

 The latter are rhombic, broader than long, with concave sides. The proximal and 

 distal extensions are about equal in size. 



The arms are smooth. Then" bases are rather close together but are not wall- 

 sided. The syzygial interval is three muscular articulations. The first brachial is 

 deeply incised by the very large backward synarthrial projection of the second brachial. 



Pi has 17-18 segments, 4 mm. long. The third or fourth segment is squarish, 

 the sixth is half again as long as broad and the longest segments are two and a half 

 times as long as broad. P? has 10 segments and is 2.5 mm. long. The third segment 

 is slightly longer than broad and the longest segment is three times as long as broad. 

 P3 has 17 segments and is 4.5 mm. long. P4 has 12 segments, and is also 4.5 mm. 

 long. Either P3 or P^ is the first genital pinnule with a small gonad. Pa \vith 10 seg- 

 ments is 2 mm. long. P^ also with 10 segments is 3 ram. long. 



The disk is 3.7 mm. in diameter and the anal cone is about 4 mm. high. 



