140 BULLETIN 82, UNITED STATES NATIONAL MUSEUM 



rarely they are at first represented by a simple transverse ridge which later divides 

 into a pair of tubercles, while occasionally there are triple instead of double dorsal 

 tubercles or spines, or rarely the dorsal processes are obsolete on the earlier segments. 

 Usually on about the sixteenth or seventeenth segment, but sometimes as early as the 

 eighth or ninth and sometimes not until about four or five segments before the penulti- 

 mate, the double dorsal process becomes a single dorsal tubercle or short spine which 

 usually decreases in size on the outermost segments and may disappear on the ante- 

 penultimate. The segments in the proximal half of the cirri are usually more or less 

 constricted basally. The opposing spine is considerably larger than the spines on 

 the segments immediately preceding, its height equaling from one-third to two-thirds 

 the width of the penultimate segment, and being most commonly about one-half. 

 The terminal claw varies from as long as to half again as long as the penultimate seg- 

 ment and is curved and sharply pointed. 



The radials are usually visible as narrow bands beyond the run of the centrodorsal, 

 but they may be wholly concealed by the centrodorsal, visible only in the interradial 

 angles, or even visible as broad bands; they are laterally united hi the proximal half 

 or more. The IBrj are from one-third again to five or even six tunes as broad as 

 long, being usually three or four times as broad as long. Their lateral edges are 

 usually slightly convergent, but may be almost or quite parallel, and are laterally 

 free. The middorsal line is commonly smooth, but may bear a slight and obscure 

 median carination. The IBr 2 (axillaries) are broadly pentagonal, from one-third 

 again to three or even four tunes as broad as long, being usually from half again to 

 twice as broad as long, and roughly about twice as long as the IBr 1( Their lateral 

 borders make a very obtuse angle with those of the IBr,. They may bear a weak 

 median carination. The IIBr and IIIBr series are 2, the latter being developed only 

 on the outermost sides of the postradial series so that the maximum number of arms 

 on a postradial series is 6, arranged in 2, 1, 1,2 order. The IIBr, are from half again 

 to twice as broad as long and may be nearly oblong, or the inner side may be shorter 

 than the outer. The division series are well separated laterally. The ossicles imme- 

 diately following each axillary are interiorly united. Slight synarthrial tubercles are 

 usually, though not always, present; rarely the synarthrial tubercles are well developed. 



The arms vary from 10 to 30 in number. Of 593 specimens examined, 124 have 

 10 arms; 61 have 11 arms; 77 have 12 arms; 51 have 13 arms; 23 have 14 arms; 19 

 have 15 arms; 20 have 16 arms; 25 have 17 arms; 20 have 18 arms; 26 have 19 arms; 

 122 have 20 arms; 12 have 21 arms; 7 have 22 arms; 1 has 25 arms; 3 have 26 arms; 

 1 has 29 arms; and 1 has 30 arms. Thus slightly over two-fifths of the individuals 

 have either 20 arms (21 per cent) or 10 arms (21 per cent), and only 62 (10 per cent) 

 have 14-16 arms. The arms vary from 25 to 95 mm. in length, being most commonly 

 between 30 and 45 mm. long (about 44 per cent of the specimens), though frequently 

 up to 80 mm. The arms are smooth, and are composed of 100-120 or more brachials. 

 The first brachials are about twice as broad as long, and are basally united interiorly. 

 The first 5 to 7 or 8 brachials are oblong, and those following are oblique!}' wedge- 

 shaped or triangular, about as long as broad, later slowly becoming oblong again 

 and terminally half again as long as broad with swollen articulations. There are 

 18-20 brachials for each 10 mm. of arm length, or 15 or 16 if the syzygial pairs are 

 counted as units. 



