78 BULLETIN 75, UNITED STATES NATIONAL MUSEUM. 



off Alaska, lat. 54 46' N.; long. 157 43' 30" W., 138 fathoms, mud, 

 gravel, bottom temperature 37.4, 1 specimen; station 5023, Okhotsk 

 Sea, lat. 48 43' 30" N.; long. 145 3' E., 75 fathoms, sand, pebbles, 

 bottom temperature 30.9, 7 specimens; station 5029, Okhotsk Sea, 

 lat. 48 22' 30" N. ; long. 145 43' 30" E., 440 fathoms, black sand, 

 gravel, bottom temperature 35.3, 4 specimens; station 5079, off 

 Omai Saki, Japan, lat. 34 15' N.; long. 138 E.,475 to 505 fathoms, 

 pebbles, bottom temperature 39.1, 8 specimens. Bathymetrical 

 range, 75 to 505 fathoms. Temperature range, 42.6 to 30.9. 

 Seventy-three specimens. 



This splendid series of specimens is of great interest in showing 

 the growth changes of one of the largest, and probably the heaviest, 

 of the simple-armed ophiurans. The smallest specimen has the 

 disk 6 mm. in diameter and nearly 3 mm. thick. It is covered by 

 about sixty plates, of which the primary plates and five additional 

 plates (one proximal to each pair of radial shields) are more or less 

 swollen and correspondingly conspicuous. In the largest specimen 

 the disk is 47 mm. in diameter and is 14 mm. thick just proximal 

 to the radial shields; it is covered by about one hundred and fifty 

 plates. While the diameter has increased about eight times, the 

 thickness has only increased five times and the number of plates on 

 the disk only two and a half times. In another specimen, in which 

 the disk diameter is about 42 mm. there are only about seventy- 

 five disk plates. In all specimens regardless of size, the radial plate 

 just proximal to the radial shields, is the most swollen and usually 

 the most conspicuous. In the largest specimen the arm is extraor- 

 dinarily triangular (in cross section) at base; each of the three sides 

 is 10 mm. across. In small specimens the arm is not so sharply 

 keeled, but it is distinctly trigonal. The arm spines show considerable 

 diversity in different individuals, quite apart from size. There was 

 only a single specimen in the Challenger collection and it is probable 

 Lyman did not dry that one completely, so that he was misled in 

 regard to the number and arrangement of the arm spines. In reality 

 we can distinguish here, as in sterea, between true and secondary 

 spines. The true spines are usually two in number, short, thick, 

 and peg-like; often there are three, frequently only one, and some- 

 times they appear to be wholly wanting. The secondary spines are 

 very flat, thin, and blunt, and first appear on the angle of the arm 

 between the lowest true spine and the tentacle scales. They may be 

 wholly wanting, especially in young specimens. In adults, they may 

 be numerous (as many as twelve) and reach clear to the top of the 

 side arm plate. Usually they are distinctly more marginal than the 

 true spines, but sometimes all are in the same plane, and then the 

 true spines can only be distinguished, if at all, by their larger size 

 and different shape. In the Challenger specimen, the true spines 



