\-n:i; i;\ 01 mmu'ii PACIFIi \\i> ADJACBNT uatkus hshkk 11 



operating together, or only in pari as sometimes occuro, effect considerable differences 



aeral appearance. 



Mm in medium-sized and large examples thai maj reasonably be regarded a- 

 inn i me there are rather striking variations. Theabactinal spines differ somewhat with 

 practically every locality, and even al t J i « - ition exhibit minor differences not 



connected with age. They vary from fairly Blender, slightly tapering, to Btout, cylin- 

 drical, or clavate. 'Die end may be merely blunt; or bifid < >r trifid; or swollen; or 

 compressed a little and therefore sometimes spatulate, usually with a faint to decided 

 groove. Such gouge-shaped spines predominate <>n the proximal part of the ray of 

 some examples which have the Bpines of the distal half more generalized. Go 

 shaped spines are rare <>n immature examples, even though the adult ha- them well 

 developed. 



The stoutness of the abactinal ossicles and the relative size of the meshes of the 

 skeleton arc variable. The skeleton is sometimes quite flaccid, but this may be due 

 partly to maceration in weak alcohol. In examples from shallow water both stout 

 (station 3231 | and relatively weak (station 3298) plates are found. The chars 

 of the bottom, and available food may affect this condition, but nothing is known 

 concerning the cause of the difference. Usually the skeletons composed "f weak 

 plates carry the small terete, unmodified spines. 



The marginal spines of shallow-water specimens seem to be at least Blight 

 shape or grooved down the outer side in mature, large examples, but the stoutness of 

 the spine, its form and the size of the groove varies greatly. In extreme cases the 

 inferomargina] spines, which may l>e taken as an index, me rather slender, tapered, 

 and only faintly grooved (Popoff Strait |, while from the same locality another It 

 specimen lias spatulate conspicuously furrowed spines relatively two to three times 

 as broad. From station 3231 see p. 19) are examples of forma anotruda having still 

 stouter more scoop-shaped spines. There is every gradation between the extremes. 



In young, the marginal Bpines are always Blender, and much more constant in form. 

 Certain specimens without reference to locality have one or two rows 



marginal spines on the proximal part of the ray, the number of spines viin Some- 



times they have the appearance of completely filling the intermarginal channel prox- 

 imal lv. This feature occurs in specimens from various parts of the range, for instai 

 southern Bering Sea, Norton Sound, Petropavlovsk, and in forms with both slender 



and very stout spines. It is present also in examples from deep water (81 fathoms, 

 station :;_'.".7 |. 



While most ,,f the inferomarginal plates carry two spines m an oblique series. 

 certain plates here and there have three in a triangular group. Frequently at the base 

 of the ray there appears to tie regularly three inferomargina] spines, hut the outer i- 

 almost always nil lut, marginal . 



The form of the subambulacral Bpines varies with that of the inferomarginaJs. 

 When the latter are strongly Bulcate, the Bubambulacrals are also more or lcs^ deeply 

 grooved. This \b well shown in examples from station 3231 (forma anomala), from 



Other parts .,f Bristol May. Popoff Strait. Norton Sound, St. Michaels, and Petro- 

 pavlovsk. The number of adaiiibuhural spines i- variable, two and three altenia 



being the maximum. < fften there are two on each plate or one and two alternating, 



with occasionally one and three. Even in large specimens the maximum number is 



