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Show 1888.] FROM TUTICORIN, MADRAS. 385 V. HOLOTHUROIDEA. 38. Haplodactyla australis, Semp. 39. Holothuria atra, Jdyer. 40. marmorata, Jdger. 41. Holothuria monacaria, Lesson. 42. vagabunda, Selenka. NOTES A N D DESCRIPTIONS. OREASTER THURSTONI. A triplacanthid form, with the spines, except the five apicals, as a rule poorly developed. R=2'7 r. Disk moderately elevated; lophial spines only just indicated ; a spinous tubercle on both supero- and infero-marginal plates, very rarely more than one; no spines on the ventral plates. The arms rather short, wide at their base; marginals about twenty, both above and below ; angles between the superomarginals, into which the pores extend. The spinous tubercles are very slight, and present no indication of becoming spines. Adambulacral spinulation triplacanthid ; spines of innermost row eight in number, diverging very gracefully, not very slender; in the middle and outer rows there are two or three spines in each cluster, and these are, as usual, much stouter; but the middle row is much more prominent than the outer. The granulation of the lower surface tends to take on a regular pattern, owing to the aggregation of the granules into tufts, in the centre of which is a spiniform tubercle. There is a plentiful supply of sessile bivalved pedicellariae. The pore-areas of the dorsal surface are very distinctly marked on and near the disk, but are rather vaguer near the sides of the arms ; there is no central apical spine; the five spines which end the lophial line are large and prominent, and have a marked tendency to double ; the other spines of the lophial line are very inconspicuous. Along either side of that line there runs a row of small tubercles; outside these there is another row which does not extend beyond the disk; the constituents of these rows are quite small and inconspicuous. Madreporic tubercle large, just outside apical region, irregularly quadrate. Colour creamy yellow. R = 130, r = 47 millim. Of the five specimens which I refer to this species three have the characters just enumerated ; the two other examples differ to a somewhat remarkable extent from what appears to be the more typical form of the species. In one the apical spines are much less prominent than in the form already described, while the tubercles on either side are much more distinctly spinose, and many of the infero-marginal plates have several spinous tubercles in a tuft. In the other specimen the apical spines remain large, while the tubercles on either side become quite prominent, and the whole appearance of the form is thereby quite altered. By many zoologists these three forms would be regarded as three distinct species ; but I do not think that anybody who knows how Echinoderms vary will regard them as anything else than varieties of one and the same species. However, there are, in this instance, |
