204 ECHINODERMA OF TH1<: INDIAN MuSEUM, PART VII, 



Thalassometra agassizil 1907. A. H. Clark, Smiths. Miscell. Coll. (Quarterly 

 Issue), vol. 50, part 3, p. 3(50. 

 Habitat. — Galapagos Islands. 

 DEPTii. — 327-782 fathoms. 



THALASSOMETRA ATTENUATA. 



Thalmsomdm altermata 1909. A. H. Clark, Proc. Biol. Soc. Washington, 

 vol. 22, p. 147. 



DESCRrPTiON.^Centrodor.sal conical, the sides slightly convex, 3 ram. broad 

 at the base and 2 mm. high, the cirrns sockets arranged in ten columns of 

 usually two each, the pairs of columns usually slightly separated radially by a 

 shallow furrow or a coarsely tubercular ridge. 



Cirri XX, 62 — 71, elongated and very slender, 50 mm. long, the longest 

 segments being twice as long as broad or slightly longer, those after about the 

 twent3r-fifth being slightly broader than long ; the segments after the seventeenth 

 or twentieth have the distal dorsal edge produced into a serrate ridge which soon 

 gives place to small carinate dorsal spines. 



Ends of the basal rays visible as small, though rather prominent, tubercles 

 in the angles of the calyx; radials just visible, or entirely concealed, sometimes 

 bearing on the dorsal surface a row of small tubercles ; IBr, very short, widely 

 chevron-shaped, the proximal and outer thirds of the distal edge somewhat 

 everted and the distal lateral angles more or less produced ; IBr^ triangular, twice 

 as broad as long, the anterior edges somewhat everted, the lateral angles more or 

 less produced; IIBr 1 (34-4), developed in two out of six specimens, the lateral 

 edges of the component ossicles more or less pi-oduced. 



Ten to thirteen arras 80 mm. to 90 mm. long, exceedingly slender, having in 

 general more the appearance of those of some slender antedonid than of those of 

 a thalassometrid ; first brachial short, wedge-shaped, twice as long exteriorly as 

 interiorly, basally united interiorly, the anterior and posterior edges slightly 

 thickened, the lateral edges somewhat produced, and the anterolateral angles, 

 both interior and exterior, more or less produced ; second brachial similar in size 

 and shape ; third and fourth brachials (syzgial pair) usually slightly longer 

 interioi'ly than exteriorly, half again as broad as to about as broad as long; next 

 three or four brachials approximately oblong, twice as broad as long, then becom- 

 ing triangular, as long as broad, distally slowly increasing in length and becoming 

 wedge-shaped, being twice as long as broad in the outer part of the arm ; synarth- 

 rial tubercles rather prominent : IBr series and first two brachials smooth dorsally 

 or with a few small low inconspicuous tubercles, usually with slightly spinous 

 lateral borders ; following braciiials with the dorsal surface studded with very fine 

 short spines or sharp lul)ereles wliieh in some specimens are nearly obsolete ; at 

 about the end of tlu' ])ro.vi!nal fourth of tlie arm the brachials begin to 

 develop prominent longitudinal striations which increase in frequency and height 



