126 BULLETIN S2, UNITED STATES NATIONAL MUSEUM 



This is the only comatuhd in the western Atlantic with more than 10 arms, all 

 the division series of 2 ossicles, the distal edges of the brachials not produced and 

 everted, and a conspicuous comb on the outer portion of the proximal pinnules. 



Descrijdion. — The centrodorsal is moderately large and thick, discoidal, with the 

 bare polar area flat or slightly convex, usually about 3 mm. in diameter. The cirrus 

 sockets are arranged in one and a more or less complete second crowded and irregular 

 alternating rows. 



The cirri are XV-XXX (rarely over XX), 15-19 (usually about 18), about 15 mm. 

 long. The first 2 segments are very short, the third is about as long as broad or 

 nearly so, and the fifth is the longest, twice as long as broad, and a transition segment. 

 The sixth segment is rather more than half again as long as broad, and the eighth and 

 following are about as long as broad or slightly broader than long. The fifth and 

 following segments have the distal dorsal edge everted, forming a straight or slightly 

 convex transverse ridge which appears as a blunt spine in lateral view. This ridge 

 progressively becomes narrower, at the same time gaining in height, so that the last 

 6 or 8 segments are provided with a moderately high terminal dorsal spine which is 

 rather blunt and arises gradually from the distal half of the dorsal surface of the seg- 

 ment. The opposing spine is low, blunt and inconspicuous, arising from the entire 

 dorsal surface of the penultimate segment. The terminal claw is longer than the 

 penultimate segment, moderately stout, rather slightly curved. The fourth-sixth 

 segments are slightly constricted centrally and have somwehat enlarged ends. 



The ends of the basal rays are visible as small tubercles in the interradial angles. 



The radials are only visible as small triangles over the ends of the basal rays. 

 The IBri are very short, oblong, from four to six times as broad as long, or even 

 broader. The IBr2 (axillaries) are short and broad, almost or quite triangular, 

 about twice as broad as long, or somewhat broader. The IBri are almost or quite 

 wholly united, but are usually separated distally by a narrow U-shaped gap. The 

 IBra are rounded laterally and usually well separated, rarely just in apposition. 

 The IIBr series are 2, present on some, rarely on all, of the rays. The IIIBr series 

 are 2, not usually present, and when found developed exteriorlj' in reference to the 

 IBr series. 



Arms 11-22 (usually about 15), from 100 to 120 mm. long. First 2 brachials 

 short, small, approximately equal in size and similar in shape, slightly wedge-shaped, 

 the first interiorly united. These are united by syzygy in arms arising from a IIBr 

 axillary, and in the interior arms from a IIIBr axillary. The third and fourth bra- 

 chials are similar to the first and second, but oblong, forming a syzygial pair which is 

 about as long as broad or slightly broader than long. The fifth brachial is approxi- 

 mately oblong, about twice as broad as long, the sixth is wedge-shaped, and the 

 seventh and following are triangular, not quite so long as broad, becoming shorter in 

 the distal portion of the arm and in the terminal portion wedge-shaped and about 

 twice as broad as long. The fourth and following brachials have somewhat promi- 

 nent distal ends beset with fine spines. This prominence of the distal ends of the 

 brachials usually increases to about the second syzygy, then remains about the same 

 to the end of the arms. It is usually slight or moderate in amount; sometimes it is 

 practically lacking, sometimes very pronounced. 



