164 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



segments of the enlarged proximal pinnules may be finely spinous but are not other- 

 wise modified. 



Description. The centrodorsal is discoidal, small, 2-3 mm, in diameter, with the 

 dorsal pole flat or somewhat convex, up to 2 mm. in diameter. The cirrus sockets 

 are arranged in a single, or more or less completely double, marginal row. 



The cirri are XVI-XX, 16-20 (averaging 18), 9-15 (usually about 12) mm. long. 

 The first two segments are short, about as long as broad or slightly broader than long, 

 the third is slightly longer, about as long as broad or a trifle longer, and the fourth- 

 or fifth-sixth or -seventh are the longest, half again to twice as long as broad. The 

 segments following decrease in length, the distal being about as long as broad or 

 slightly longer than broad. The longer earlier segments are strongly constricted cen- 

 trally with swollen and prominent ends, this feature diminishing on the distal 

 segments, which are somewhat compressed laterally with the distal ends more promi- 

 nent on the dorsal than on the ventral side. The opposing spine is stout and promi- 

 nent, and its height is equal to about one-third the width of the penultimate segment. 



The radials are almost entirely concealed by the centrodorsal ; their distal border 

 may be plain, or it may be adorned with small tubercles. The syzygial pair repre- 

 senting the IBr series is about three tunes as long as the radials. The elements of the 

 IBr series bear a weak median prominence. 



The five arms are 25-95 (averaging 70) mm. in length and are composed of about 

 120 brachials. The first brachial is short and oblong and bears no pinnule, and the 

 next four or five are nearly oblong, slightly shorter on one side than on the other, 

 the longer side being shorter than the width and bearing a pinnule. The eighth and 

 following brachials have more markedly unequal sides, the longer of which is longer 

 than the width. The brachials in the middle of the arm are nearly square, and the 

 terminal brachials are elongated. Feeble articular tubercles are sometimes evident. 

 There may be ventrolateral rows of small tubercles as far as the fourth brachial. 



Syzygies occur between brachials 3 +4, 8+9, and 13 + 14 (rarely between brachials 

 12 + 13) and distally at intervals of 3 muscular articulations. 



P c is 4 mm. long with 10-12 short segments of which the basal are rather broad. 

 P! is similar to P c but usually slightly longer and stouter. P a is 6-7.5 mm. long, 

 with 10-17 (usually 10-12) segments, very much longer than the preceding pinnules, 

 with longer and more massive segments. P 2 is 6-8 mm. long and resembles P a . P b 

 and P 3 are much slenderer than the preceding pinnules and have the outer segments 

 from two and one-half to three times as long as broad. The distal pinnules are about 

 9 mm. long with 15 segments. The pinnules from P c to P 2 are extraordinarily stout 

 and thick and are sharply triangular in cross section. The third segment of P! and 

 P, is about as long as broad, and the distal segments are three-quarters again as long 

 as broad, without distal spiny edges. 



The disk is completely plated, entire, and up to about 3 mm. in diameter. Sac- 

 culi are fairly closely set on the arms, but much larger and more closely set along the 

 sides of the pinnule ambulacra. 



Notes. In the specimen from Bock's station 59, as described by Gisle'n, the cen- 

 trodorsal is 3 mm. in diameter with the bare dorsal pole, which is somewhat convex, 

 2 mm. in diameter. The cirri are XIX, 19-21, from 11 to 15 mm. long, arranged in 

 a single or double row. The first-third segments are short, the fourth-seventh are 



