in 'I '. "i NORTH I'M ii i' \M> UJJACENT WATERS FISHER U 



their appearance in No. 2, and in No. 3 tl I- half the length of 



In No. :> tin' Buperomarginal 9pines have increased to two or three; in Nos S and 8, 



three is the commonest number, occasionally four, while i r 1 No 8, four or 



found. 



No. 1 and No. 2 have proximally two, then alternately "tic and two, adam- 

 bulacral apinee, and while the plates upon which the Inter furrow Bpine will -• 

 ciin be recognized, the Bpine itself is not yd differentiated from the other- This i- 

 very definitely beginning in No. '■'>, and the spines are well differentiated in \ 

 Adambulacral spinal pedicellariae appear firel in N 



The simiU specimens have no actina] plate-. In Nos l ami •_' there i- only 

 on'' pair of adambulacral plates in contact behind the mouth plate-: h 



there are three, ami in No. in there are five. 



In No. 8 tli«' Buperomarginal, inferomarginal, and Bubambulaoral spines show 

 the beginning of a definite -hallow groove on the outer Bide, and the marginal spi 

 are slightly broader toward their rounded tips. Considerably ■ 

 for instance 9 and 10, may have narrower marginal spines; and the Bubambulacral 

 spine- are |e<s evidently grooved — in fact the furrow -hows faintly at the top only. 

 The amount of grooving, after the animal reaches the age when it should appear, i- 

 nol dependent upon size alone, hut is subject to a very wide range of variation often 

 in specimens from the same station, as in the case of the Petropavlovsk examples 



Anatomical notes.- Skeleton: As noted under description and variations then- is 

 dderable diversity in the stoutness of the skeleton enough certainly to justify 

 the assumption of more than one species if only a few isolated extn re avail- 



able. The -keieion : Uj heavy in forn ■!". 



The abactinal skeleton is the open irregular mesh type of rubens, with usually 

 an irregular carina! plates forming a wavy line along the radius. The 



plate- of the dorsolateral regions have generally three irregular lobes, or three -id( -, 

 while the carinals Btart out in small specimens fairly regularly four lobed but 

 irregular with age. The 3-sided dorsolateral plates stand at the nodes of the net 



while the connecting bars ar mposed of one or two narrowly to broadly elliptical 



overlapping ossicles, some of which hear a single small Bpine. The primary pi 

 usually hear a single spine, but some of them especially in the carina! Beries bear 

 two or three. The breadth of the abactinal plates ami the degree of overlapping 

 determines the openness of the skeleton. The number of the meshes from one side 

 of the ray to the other varies with age, and is difficult to count accurately perl 

 12 to ll i- a fairly correct estimate for medium-sized specimens. 



The Buperomargina] plates s| ;i rt out in young specimens in the normal 4-lobed 

 form for the family hut the dorsal lobe is later suppressed, while the ventral 

 less conspicuous as the plate lengthens, until a s,,rt of lozenge form results Tin' 

 plates are strongly imbricated with tin' adoral end outside The inferomarginals 

 are larger, more definitely four lobed, and an ted with the superomaxginals 



by from one to three overlapping ossicles except distally and in young specimi 

 ries of these intermarginal ossicles may hear solitary -: 

 proximally. (Normally the plates adjacent to inferomarginals hear a ~hort - 

 at base of ray i The actina] plates ar.- inconspicuous except near the mouth p] 

 there is a single incomplete Beries, which appears rather late, and ti 



