ASTEROIDEA 91 



specimens from 1 27 fathoms are referable to the Antarctic form, and I have confirmed 

 this by an examination of an example from the type locality, Challenger St. 149H. 

 Although this specimen is small (R 47 mm.) it shows the characteristics of the Antarctic 

 form rather than of loripes. 



Since both forms are variable in the robustness of ray and the rather confusing 

 matter of marginal spinules, the most constant difference seems to be the greater 

 number of marginal plates in obesus. In two specimens, each having R 107 mm., 

 obesiis has 127 marginal plates while loripes has 70. These short marginal plates are well 

 brought out in Koehler's figures. In general, Sladen's observations hold good. He says, 



P- 243 : 



" The rays are rather more distinctly cylindrical, the union of the abactinal and lateral 



areas being less angular and less conspicuous. The abactinal area is habitually much 



more inflated which gives the variety a conspicuously puffed up appearance. The small 



isolated spinelets or enlarged squamules on the marginal plates are smaller and less 



developed; and in young examples may be absent altogether from the inferomarginal 



plates and represented on the summit of the superomarginal plates by a squamule only 



very slightly greater than those forming the rest of the covering of the plates." 



The specimens from St. 458, Bouvet Island, 357-377 m., are clearly obesus, as are 

 those from South Georgia. Large specimens from South Georgia, the Palmer Islands, 

 and South Orkneys have a very small superomarginal spinule at the upper end of the 

 plate and also a second at about the middle ; while the inferomarginals carry, proximally 

 3 or 4 small appressed sharp spines in a vertical series and distally 2 or 3. Two very large 

 specimens, from St. 1660, Ross Sea, have R 204 mm. and 175 mm., r 32 mm., and are 

 comparable to Koehler's largest example from Adelie Land, in which R is 170 mm., 

 r 35 mm. (Koehler, 1920, p. 263). There are usually 3 sharp superomarginal spinules 

 and 3 or 4 inferomarginal, very closely appressed to the plates but obviously larger than 

 the rounded squamules covering the plates. A large specimen from St. WS 27, South 

 Georgia, 106-109 m., gravel, has R 160 mm., r 25 mm., and 3 superomarginal spinules 

 in a vertical series, easily distinguished from the broad, rounded squamules covering the 

 plate by their slightly greater length and sharp points. The proximal inferomarginals 

 have usually 4, and the distal inferomarginals 3, similar enlarged spinules. 



For purposes of recognition the following points may be stressed. The rays of obesus 

 have more rounded sides, and there is a less evident angle of demarcation between the 

 lateral and abactinal surface of the ray, which (especially in the high Antarctic specimens) 

 is inflated or " puffed up ". But the rays are not broader at the base in medium-sized and 

 large specimens. All the marginal spinules are smaller in obesus, the uppermost supero- 

 marginal spinule being very small, or absent. The abactinal paxillae of obesus "run" 

 slightly smaller than in loripes, but are not invariably so, for in a specimen from St. 167, 

 South Orkneys, with R 140 mm., they measure very close to the paxillae of loripes from 

 St. WS 819. The number of marginal plates is a very tangible character when there are 

 specimens of loripes for comparison. 



Type locality. Challenger St. 149H. Off Cumberland Bay, Kerguelen Island, 127 

 fathoms, volcanic mud. 



