122 CLARK : NEW GENERA OF ECHINODERMS 



The anal opening, which is large and surrounded with short spines, 

 lies near the apical spiniferous plate. 



The madreporite is a separate skeletal element lying between the 

 plates of the first pair below the large lobate plate at the base of the 

 interradial area. 



The superomarginals are trilobed and strongly imbricating; in the 

 proximal two thirds of the arm the imbrication is toward the center of 

 the interbrachial arc, in the distal two thirds it is toward the arm tips; 

 a quadrilobate plate imbricating both ways marks the transition. 



Except for slightly greater size the inferomarginals are not different 

 from the plates forming the outermost row of the actinal intermediate 

 series, just within them; they are much broader than long in the 

 interbrachial arc, but increase in length outwardly; their imbrication 

 which is slight, is outward. Each inferomarginal bears a prominent 

 flattened spine with a truncated gouge-shaped tip, except for the three 

 or four in the center of the interbrachial arc which bear two similar 

 but smaller spines. 



The actinal intermediate plates are elongate, imbricating adcentrally, 

 arranged in regular bands between the inferomarginals and the adam- 

 bulacrals which correspond to the former but not to the latter. The 

 plates composing these lines form about five regular transverse rows. 

 The row adjoining the inferomarginals has an additional plate in the 

 center. There are no actinal papulae. 



The aclambulacral plates have a prominent, slender, sharp-pointed 

 spine deep in the furrow, and a much longer and stouter chisel-shaped 

 spine with a truncated gouge-shaped tip on the inner border of the 

 actinal surface; in the terminal portion of the arm there are two of 

 these latter to each plate instead of one. 



The mouth plates bear two long flattened spines distally, which 

 increase in diameter to the truncated tip, and a similar spine at the 

 border of the first adambulacrals. 



Glabraster magellanica (Studer) is confined to the Magellanic region, 

 occurring in the Straits of Magellan and along the shores of Patagonia 

 from the shore line down to 45 fathoms; Glabraster antarctica (E. A. 

 Smith), the only other species of the genus, is known from Kerguelen, 

 Marion Island, Prince Edward Island, the Crozet Islands, and South 

 Georgia, in from 50 to 1600 fathoms. 



