88 



being rather sinuate; there is sometimes a distinct transverse line over the outer 

 part of the genital plates. The genital opening is placed almost in the middle of the 

 plate. One or two small tubercles are found at the inner edge of the genital plates 

 and one in the middle of the ocular plate. 



The buccal plates may be placed one outside the other in each pair or 

 equally distant from the edge. The plates along the inner edge of the buccal mem- 

 brane are very faintly developed or even totally wanting, and the same holds good 

 for the bihamate spicules. — The spines are short, the longest being about half as 

 long as tiie diameter of the test; they are slender, not widened at the point, except 

 those at the peristome, which are flattened and a little widened, and also a little 

 curved. The primary spines are more or less thorny, sometimes, however, quite 

 smooth, though — so far as my experience goes — never all of them in the same 

 specimen; the secondary spines (Fig. 5) are generally more thorny, ending in a large 

 central thorn, surrounded by small ones at its base. 



The globiferous pedicellariæ (PI. VI. Fig. 13, PI. VII. Fig. 25) have no lateral 

 teeth, only a rounded knob on each side below the endtooth. The outer corners 

 of the basal part are sharp and generally a little produced. The ophicephalous 

 and triphyllous pedicellariæ do not difl'er from those of siamensis. — Spicules 

 I have not seen in the tubefeet, but at the base of the spines some few may 

 be found. 



The colour is rather variable: whitish with faint brownish spots, which are 

 often most prominent between the primary tubercles in each series, or brown with 

 a white spot in each area near the ambitus; the inlerambulacra may be darker 

 coloured, forming thus a starshaped figure on the upper side of the lest, as may 

 also be the case in siamensis. The genital plates are mostly white in Die middle, 

 the edge being brown; in lighter coloured specimens tliere is only a brown spot at 

 the two inner corners and one at the outer end of the plate. The primary spines 

 are whitish with one or two faintly reddish bands. 



This very small species (the largest specimen, I have seen, is 9 mm. in 

 diameter) is evidently very widely distributed in the Indo-Pacilic Ocean, being known 

 from the Red Sea, the Persian Gulf, the Malay Archipelago and New Britain. For 

 the localities where it has been dredged by the „Siboga" reference must be made 

 to DE Meliehe's work (p. 202). — It is evidently most nearly related to sianwnsis, 

 from which species it is, however, easily distinguished, mainly by its thorny spines 

 which are not thickened at the point. Specimens like those from Muscat otherwise 

 may look very like siamensis. The large anal plate is a very interesting feature, 

 and the reticulate condition of the plates and tubercles reminds one of Genocidaris, 

 showing thus that the reticulate or grooved condition of the ])lates is no exclusive 

 character of such genera as Trigonocidaris and (leiwcidaris. (Comp, below: the 

 classification of Ihe Ti'innonlcurids.l 



