222 ECHINODERMA OF THE InDIAN MtJSEUM, PART VII. 



PACHYLOMETRA MACILENTA. 

 Pachylometra inacilenta 1909. A. H. Clark, Proc. Biol. Soc. Washington, vol. 



22, p. SI. 



Description. — Centrodorsal a short truncated cone, moderately large, the 

 bare polar area flat, 25 mm. in diameter: cirrus sockets arranged in ten columns 

 of usually two each, the columns of adjacent radial areas closely crowded and 

 more or less alternating, those within the same radial area usually slightly sepa- 

 rated anteriorly. 



Cirri XX, 21 — -22, 25 mm. to 36 mm. long, comparatively long and .slender : 

 first segment very short, second twice as broad as long, third about as long 

 as broad, the following gradually increasing in length to the sixth, which is 

 about half again as long as broad ; next two or three segments similar, the 

 following very gradually decreasing in length, those in the terminal third of the 

 cirrus being about as long as broad ; antepenultimate segment about one third 

 longer than broad; penultimate segment half again as long as broad, slightly less 

 in diameter than the preceding ; opposing spine very small, though prominent, 

 terminally situated , directed obliquely forward ; terminal claw about as long as 

 the penultimate segment, stout basally, but becoming slender in the distal half, 

 moderately curved. The cirri are moderately compressed in the distal two 

 thirds ; the two or three segments before the penultimate have slight traces of 

 terminal dorsal tubercles. 



Disk covered with a pavement of very small plates ; side and covering plates 

 well developed along the ambulacra. 



Ends of the basal rays visible as large rhombic tubercles in the angles 

 of the calyx ; radials only visible as a large transversely oval tubercle 

 between the centrodorsal and the IBr^ ; IBr, very short, arcuate, in close lateral 

 apposition, the proximal edge more or less crenulate and bearing a large and 

 rather high transversely oval median tubercle ; IBr, rhombic, very short, some- 

 what over twice as broad as long, the edges somewhat crenulate and somewhat 

 produced, the proximal imbricating more or less over the anterior border of the 

 IBr, ; the lateral edges are very short, in close apposition ; it bears a rather 

 large and high rounded median tubercle ; IIBr i (3-|-4), in close lateral apposi- 

 tion and sharply flatttened, with the lateral edges slightly everted: the distal 

 edge of the IIBr, is somewhat everted, and the proximal edge of the IIBr^ more 

 strongly everted, the latter imbricating over the former except in the median 

 line; the IIBr, usually bears a strong rounded median tubercle hke that on the 

 two components of the IBr series. 



Thirteen arms (in the type) 170 mra. long, elongated and comparatively 

 slender, resembling those of P. robusta 



The pinnules in general resemble those of P. rohusta ; the pinnules in the 

 proximal part of the arm are strongly carinate. . 



The colour in spirits is white. 



