ASTKHOIDKA 01 WORTH PACTFII V\|i Vh.lMI.VI USIM;> IISIIKU IVA 



In the order of their degree of differentiation from typical polaria, the formae 

 stand as follow - : 



1 . Abaotinal Bpines -mull, close-eel . of nearly uniform size, « ithoul regularity of 

 arrangement and without any trace oi aggregation into canvas groups apkdonota. 



2. Abactinal surface with a variable Dumber <>f convex groups of spines often 

 in three ill-defined longiseries), the Bubcentral spine of the group usually larger than 

 the others acervata. 



Abactinal surface with large, conical or acorn-shaped Bpines, typically soli- 

 tary, in twos or occasionally larger groups, arising abruptly from an irregularly 

 reticulate Bpinulation of small, capitate, unequal Bpinelets polythela. 



The type of Leptasteriaa •polaria acervata is No. 1336, U. S. National Museum, 

 Bering Strait, clean gravelly bottoms, 5 to Lfi fathoms. I Further details under forma 



aia. > 



I ..mi .. Mill I nSO I V. n.» form* 



Plate 31, Figures 2, 3a, 36, I; Plate 32, Figure I. I 



Plate 36, Figu 



This forms is based upon a giant specimen from Btation 2850, oil' the Shumagin 

 fslands, 21 fathoms, which Iims the following characters: K 245 mm., r ll mm., 



r 6 r; breadth of ray at base 13 mm. Kays long, rather slender evenly tapered to 



the pointed extremity; rays constricted at base; disk rather small; interbra 

 Bulcus bidden bj contiguous sides of adjacent rays; abactinal Burface of rays well 

 arched, closely studded with small, bluntrj pointed or obtuse Bpines of pretty uni- 

 form length, arranged in loose groups of two or three to eight, corresponding to the 

 size of the underlying plate; papular areas small; abactinal plates verj numei 



closely and irregularly reticulated: BUperomSXginal spines in vertical COmbs 

 groups of three lo si\, usually four, to a plate; infe romai'trimd spine- two or three to 

 a plate, conspicuously longer and heavier than the superomnririnals. which in turn 



are slightly longer than the dm-. 'laterals; two series of actinals, similar to inf 

 marginals; adambulacral plates diplacanthid; dermal Btraighl pedicellariae sub- 

 corneal to broadly wedge-ehaped with five teeth similar in general appearance to 

 those of act rvata. 



/'> a ption The well-arched aliactimd Burface is closely beset with uniformly 

 small Bpines of nearly equal length but of unequal thickness, arranged without any 

 order, in loose groups, running into one another, and inclosinLr relatively ?erj smnll 



papular areas. Reference to a cleaned ray shows that these groups correspond to 

 the larger, primary, abactinal plates, which (any five to seven -pine-, while the 

 smaller intermediate plates calTV one to three The -pine- ale therefore arranged 



in a close reticulum but this is masked by the very numerous abactinal plat 



smallne— of the lnc-he- of the skeleton, their irregularity, and by the fact that the 



-pines nil' in groups, not in single file. The Bpines v arj considerably in form, hut are 



usually cylindrical at the base with a slightly swollen, tapered, coarsely sulcated, 



bluntly pointed or round tipped end Others, especially on the disk and -id. - 



the i ather more elongate ami more pointed than the majority from the median 



radial area of the rav : and on the outer third of the radial area the spines are hlunter 

 than they are pro\imallv I hie and there a spine is perhaps a third longer and 



iderably thicker than the average which are 2 to 2.5 mm. long and l mm. thi 



