OCR Text |
Show 100 ZOOLOGICAL COLLECTIONS MADE DURING [Jail. 4, there are, however, about twice as many of these projections in the interradial as in the radial bands. There are no spines or other processes on the dorsal aspect of the arm, which is only closely granulated; no indication of any banded arrangement of the granules in correspondence with the joints of the arms can be made out till the third bifurcation is passed. The tentacle-scales are ordinarily arranged in fours, and are short, spiniform, and subequal; the pore nearest to the mouth seems to be always without the scale; the next may or may not have one ; the third has one ; the fourth or fifth pore has two, the seventh or eighth three, and the tenth or eleventh four. The arms completely white, as are the radial ribs and the edges of the genital slits ; the rest of the disk is of a brown colour, which is relieved by the white spinous granules. The smaller of the two specimens of A. pourtalesi (Lyman) had the diameter of its disk (63 millims.) nearly 20 millims. longer than the specimen now under examination ; and it is possible that the affinity between the two species may hereafter be shown to be closer than we are yet justified in supposing it to be. Whatever the result, the suspicion induces me to place with A. lymani a second and smaller example of the same genus. It is to be distinguished from it by several points, but every one of them may, I think, be more rightly ascribed to differences in age and in sexual condition than to inherited distinguishing characteristics :- (1) The mouth-slits are very distinctly rounded ; and the whole actinostome forms a rosette. (2) The interbrachial spaces are sharply incised at the edge of the disk. (3) The radial ribs, though distinct, are not prominent; and the granulation on them and on the interradial spaces of either surface is less differentiated than in the larger form. (4) Transverse bands of granules can be detected on the dorsal surface of the arms quite close to the disk. (5) The fifth difference lies in the smaller number of the tentacle-scales ; and that is one of far greater importance than any of the preceding differences : most of the tentacle-scales are arranged three in a row. Perhaps a larger series may, contrary to what ordinarily happens, enable us to definitely distinguish, the two forms. The larger specimen was taken in' Trinidad Channel, at a depth of 30 fathoms ; bottom, sand. The smaller at Port Rosario, 2-30 fms. ; bottom, sand and rock. HOLOTHUROIDA. As I have already remarked, this class is very feebly represented. I have here only to direct attention to two species. CUVIERIA ANTARCTICA. This species, first described by Philippi (Arch. f. Nat. 1857, p. 133), has since been recorded by Studer (Monatsb. Ak. Berl. |