ASTEROIDEA 167 



The largest specimen, St. 39, measures R 17 mm., r 5 mm., br 5 mm. Koehler (1923) 

 records 2 specimens from Shag Rocks, 160 m., having R 30 and 36 mm. It is probable 

 that the species never attains a size comparable to that of obesa. Rays slender to medium 

 robust. 



The adambulacral armature consists of a transverse series of 4 or 5 prominent sub- 

 ambulacral spinelets, decreasing in length from furrow outward, and in addition i, or 

 occasionally 2, shorter, but still prominent spinelets deep in furrow. The subambulacral 

 spinelets are the longest on the body. The consecutive series are well spaced from one 

 another and constitute a conspicuous cheval-de-frise all along the furrow margin. The 

 single series of actinal plates extends to middle of ray and each carries i to sometimes 

 2 or 3 delicate spinelets, shorter than the outer subambulacrals (and much shorter than 

 the longer furrow members of series). The marginal plates do not form very regular 

 series. The inferomarginals carry 3-5 short spinelets in a transverse series or a group, 

 while the superomarginals (not always recognizable) are like the abactinals and carry 

 usually 1-3 short spinelets in irregularly spaced groups. 



The papulae are dorsally i or sometimes 2 to each mesh of the skeleton ; laterally and 

 ventrally they are single, and extend to the adambulacral plates, adjacent to which there 

 is a regular series for the entire length of the ray. (This series is entirely lacking in the 

 fine specimen of simplex from Marion Island. In this the papulae do not cross the infero- 

 marginal plates, there being no true actinal papulae.) 



The tiny specimen from Tristan da Cunha has R 6 mm. and r 2 mm. It has actinal 

 papulae and is not distinguishable from an equal sized specimen from St. 140. 



Mortensen (1925, p. 304, pi. 13, figs. 1,2) has given notes onH. Mm«Y of the Auckland- 

 Campbell Islands and has differentiated it from pagenstecheri. It is probably a valid 

 "small species ", but it is only fair to record that some of the peculiarities of hikinsii are 

 not so apparent when a good series oi pagenstecheri is examined. For instance, in the 

 latter the spinelets of the proximal marginal plates often form transverse series with 

 those of the adambulacral and actinal intermediate plates. The true furrow spine of 

 pagenstecheri is not always directed horizontally but may be bent upward (as viewed 

 from actinal aspect). There is sometimes (e.g. St. 25) a conspicuous actinal interradial 

 naked area, or slight depression, in the angle outside the oral plates, as stated by 

 Mortensen, but this area may also be nearly or quite obliterated by small spinelets, 

 singly or in twos (Sts. 39, 123). The rays of lukinsii are stouter and the disk larger than 

 in any of my specimens of pagenstecheri. 



In spite of these apparent discrepancies I agree with Mortensen that there is an 

 average difference between the two forms both of which are small in size and hence most 

 difficult to evaluate accurately. 



Type locality. South Georgia. 



Distribution. South Georgia, Shag Rocks, Tristan da Cunha, 18-250 m. 



13-2 



