636 PROCEEDINGS OF THE NATIONAL MUSEUM. tol.xxxvi. 



the arm oblong and very short, though somewhat longer again 

 terminally. The proximal discoicli\l brachials are somewhat swollen, 

 and most of the brachials have slightly overlapping distal ends. 

 Syzygies occur between the third and fourth brachials, again be- 

 tween the thirteenth and fourteenth to thirty-first and thirty-second 

 (usually somewhere between the sixteenth and twenty-fifth, with 

 sometimes an extra one from two to four or five brachials beyond 

 the first), and distally at intervals of two to thirteen (usually eight 

 to twelve) oblique muscular articulations. 



Pd T mm. long, moderately stout basally, but tapering rapidly and 

 Ijccoming slender in its distal half, with about twenty-five joints, at 

 first three times as broad as long, becoming twice as broad as long at 

 the sixth, and squarish in the terminal portion; some of the lower 

 joints are bluntly carinate; P^ 10 mm. long, with 30 joints, slightly 

 less stout basally than Pd and tapering somewhat less rapidly; joints 

 at first about twice as broad as long, becoming as long as broad at about 

 the eighth, and somewhat longer than broad terminally; P„ 15 mm. 

 long, stouter than P,, tapering evenly to a delicate tip, with 30 

 joints, at first about half again as broad as long, becoming squarish 

 at the eighth or ninth, and about twice as long as broad at the tip; 

 P.; 22 mm. long, stouter than the preceding, with 30 joints, at first 

 broader than long, becoming squarish about the tenth, and longer 

 than broad terminally; the pinnule is more or less carinate in its 

 proximal half and has a moderate supplementary ridge on the distal 

 half of the outer side; P4 resembling P., but very slightly longer and 

 slightly stouter and more carinate; Pr, like P;j; P^ 10 mm. long, re- 

 sembling Pj, but somewhat more strongly carinate proximally; fol- 

 lowing pinnules gradually decreasing to 7 mm. in length and losing 

 the basal carination, then increasing to 12 mm. distally. On some 

 arms Pr, is small as described for P,.,, and again P^ may also be small, 

 while occasionally P. and P^ are similar and P;, is greatly enlarged; 

 sometimes PP., o, and ^ are as described for PP.,, 4, and 5. On one 

 or more of the inner arms of each ray P.j is often much larger than 

 on the outer, while the adjacent ])innules are reduced. 



Type-Specimen. — Cat. No. 42B., Indian Museum; Port Blair, 

 Andaman Islands. 



rofype.—Q'Ai. No. 25470, TT.S.N.M.; from the same locality. 



T have dedicated this species to Dr. Th. Mortensen, of Copenhagen, 

 in recognition of his valuable contributions to the knowledge of the 

 Echinoderms. 



Genus HETEROMETRA A. H. Clark. 



HETEROMETRA COMPTA, new species. 



Centro-dorsal discoidal, the bare polar area flat, slightly convex or 

 slightly concave, about 5 mm. in diameter;. cirrus sockets arranged 

 in a single more or less irregular marginal row. 



