142 DISCOVERY REPORTS 



St. 182 (Fig. B, 4-4C). This specimen is heavily parasitized by an organism forming a 

 large cyst at base of ray opening by a small actinal aperture. The largest cyst measures 

 15 by 10 by 10 mm. There are at least 6 of these parasites, yet the gonads are well 

 developed. Experience has shown that sea stars parasitized by Dengrogaster may suffer 

 an abnormal reduction of skeleton, yet this individual appears to be normal except for 

 distortion caused by the cysts. 



R 53 mm., r 16 mm., br about 18 mm. Since this specimen was dredged in the same 

 general locality as the two small examples of antarciiais it would be rather natural to refer 

 it to that form. But the paxillae are entirely different, having the elongate pedicels and 

 slender longer spinelets of sladeni. The pedicels are commonly 0-45-0-5 mm. high, 

 while the spinelets are o-6-o-7 long. They are even less robust than those of the Shag 

 Rocks specimen. This is true also of the unmodified actinal spinelets, the differences 

 being best appreciated by a comparison of figures. A considerable number of actinal 

 plates (as in the Shag Rocks specimen) have actinal pedicellariae composed of 2 or 3 

 modified spinelets bent toward one another (fig. 4c). 



The inferomarginal plates are not clearly difl^erentiated ; nevertheless, the limits of the 

 actinal intermediate areas can be traced from the fact that the abactinal paxillae are in 

 contact whereas the actinal are slightly spaced. The former carry 2-6 spinelets which 

 appear paxilliform on account of the sacculus. Very little skin is visible between the 

 paxillae. The madreporite is small — 2 mm. in diameter. 



The adambulacral spinelets are tapered, pointed and provided each with a pulpy 

 investment. The furrow spinelets are therefore not flattened and spatulate as is rather 

 characteristic of the Shag Rocks specimen. 



The ambulacral furrow is narrow and the podia strictly biserial. 



Koehler^ has described Perknaster aurantiacus from the vicinity of Adelaide Island 

 and Alexander I Island, 92-254 m. Subsequently (1923) he recorded the same species 

 from Shag Rocks and South Georgia (Cumberland Bay), 75-160 m. The type measured 

 R 25 mm., r 6 mm. It is barely possible that the northern examples belong to P. sladeni. 

 But the type does not have longish spinelets. Koehler states: "On n'aper^oit qu'un 

 recouvrement de petits piquants serres, tres courts, cylindriques, tres legerement 

 renfles a I'extremite, qui prend la forme d'une petite tete arrondie, et pas beaucoup plus 

 longs que hauts ; ce sont plutot des granules allonges que des piquents. On ne reconnait 

 aucun groupement parmi ces piquents, que restent parfaitement isoles les uns des autres, 

 tres rapproches mais non contigus." He says further that the actinal spinelets are also 

 short. These observations having been made from a dried specimen are doubly signifi- 

 cant since desiccation emphasizes the pedicels and slender spinelets of sladeni and 

 georgianus. By no stretch of the imagination can the spinelets of these forms be con- 

 sidered "elongated granules". 



The relationship of sladeni and georgianus is a puzzle. The pedicel of the abactinal 

 paxillae of georgianus is about midway between that of sladeni and antarcticiis, yet 

 sladeni probably occurs at South Georgia in nearly the same depth as georgianus. The 

 1 Koehler, 1912, p. 36, pi. 3, fig. 9; pi. 4, fig. i ; 1923, p. 73. 



