64 BULLETIN 76, UNITED STATES NATIONAL MUSEUM 



doubtless find a chain of closely related forms connecting antarcticus with megalabis, 

 just as we are pretty certain that there is a continuous distribution of Pedicellasters 

 from southern California to Japan. Clark 18 has stated the case for Florometra, where 

 the greater number of species furnishes more striking evidence. I think it not unlikely 

 that P. typicus is derived from a distinct line of forms via the South Atlantic and is 

 not at all a small offshoot of magister as might at first sight seem probable. The 

 major crossed pedicellariae, although keeping the characteristic generic form, are 

 rather more different from those of magister than are the homologous pedicellariae of 

 jormatus. Pedicellaster pourtalesii Perrier is one of the forms of the Atlantic cycle. 



The stomach of a specimen from station 4786 was full of gastropods, the largest 

 7 mm. in diameter. 



PEDICELLASTER MAGISTER MEGALABIS, new subspecies 



Plate 16, Figure 4; Plate 26, Figures 3, 3a-3e; Plate 27, Figures 4, 4a; Plate 28, Figure 2; Plate 34, 



Figures 2, 3 



Diagnosis. — Differing from Pedicellaster magister in smaller size, decidedly more 

 delicate plates, and more open skeleton; in the larger size of the crossed pedicellariae 

 and in the presence of numerous much larger adambulacral straight pedicellariae 

 proximally, as well as in the greater distance of the gonads from interbrachial angle. 

 Type: R 43 mm., r 6 mm., R = 7 + r; breadth of ray at base, 6.5 mm. Rays slightly 

 swollen above base, slender, gradually tapered to a bluntly pointed extremity; body 

 wall weak; plates and spines invested by a thin membrane. 



Description. — None of the specimens of this race are so large as the maximum of 

 magister. The largest example from station 3347 has R 48 mm. and another from 4427 

 has R 40 mm. Alcoholic specimens can generally be recognized by the much larger 

 meshes of the skeleton and the thinner membranes covering the plates, while if two 

 equal sized specimens are placed side by side the actinal major pedicellariae of the 

 southern form are seen to be much larger. 



The skeleton is arranged as in the northern race but is much more delicate, as 

 can be best seen from the figures. The difference is as well marked in young as in 

 adults and is probably correlated with the greater depth of the habitat. The skeleton 

 may be described as open and more loosely joined than in magister. The actinal 

 plates form similar transverse series, a maximum of six plates occurring in the largest 

 specimens. The plates bear a single, generally three-pronged spinelet, about 0.5 mm. 

 long, and averaging a little slenderer than those of magister, as would be expected 

 from the more delicate skeleton. 



There are two very slender, tapered, sharp adambulacral spines in an oblique 

 transverse row, the furrow spine a little aboral to the other and a trifle shorter 

 and slenderer. On the furrow face of the proximal plates is a broadly lanceolate, 

 small pointed straight pedicellaria (0.45 to 0.48 mm. long). The oral plates generally 

 carry a row of three sometimes four slender spines, and on the surface of the plates 

 one to three straight pedicellariae like those of the adambulacrals. 



Papulae are one, occasionally two, to each skeletal mesh. 



The crossed pedicellariae are of two lands, both of which are very similar to those 

 of the northern race yet differ in respec t to size and details. The minor pedicellariae 



'« A. H. Clark. The Circulation of the Abyssal Waters of the Oceans, as indicated by the Geographical and Bathymetrlcal 

 Distribution of Recent Orinoids. Bull. inst. oceanographique, No. 285, February, 1914. 



