OCR Text |
Show 1896.] OF THE GENUS SERGESTES. 961 the one margin furnished with extremely short spines or almost naked, while the other margiu of the sixth joint and at least of the distal half of the fifth joint is armed with rather numerous spines, some of which are very long and rather robust. The differences in the armature, especially of tbe sixth joint, yield very good characters for the species. (The distal part of the fifth joint is most frequently cut off by a secondary articulation.) The eyes are middle-sized, the supraocular aud hepatic spines well developed. In the antenn. ped. the first joint is very little longer to somewhat shorter than the third joint, which is slender and obviously longer than the second. On the third joint or trl.1 and trl.2 the processes represented by Kroyer in S. edwardsl (tab. iv. fig. 9 / and 9 g) are well developed. The branchial formula as in S. atlanticus, M.-Edw. (see above) ; the branchiae above the trunk-legs are very long, above trl.3 one branchia and a lamella; trl.4 2 branchiae, the first of which is about as long as the preceding, the second somewhat shorter and only half as broad, but yet very well developed. The exterior margin of the ext. br. of urp. without any spine or tooth at the proximal end of the ciliated part. S. edwardsl, Kr.-Kroyer in his representation (p. 246, tab. iv. fig. 9, a-k) mentions a variety with longer rostrum, but this belongs to another species, viz. S. penerinki, Bate, H . J. H . The species is easily distinguished from all the other species by tbe character given in m y tabular view: that the ext Dr. of urp. has the exterior margin ciliated along its whole length-and besides by the following features in the structure of mxp.3 The sixth joint of this pair is divided into 4 subjoints about equal in length, and each of the 2 distal subjoints Is rather or verg distinctly divided into 2 subjoints, thus in all 6 subjoints; the joint ends with 2 spines of equal or different length, but at least the one is very long; next its interior margin is furnished with 35-38 spines of very different lengths (and the apical spine on the first, second, and fourth of the 6 subjoints is exceedinglv long); besides a verg long spine Is present on the same three subjoints on the one side near the exterior margin. The fifth joint of mxp.3 also presents some characters, which, however, are omitted. The rostrum is shorter than in the other species of the group, laterally compressed, and seen from the side more or less plainly forming an oblique triangle.-Length 14- 21-5 m m. I have seen specimens from the Atlantic northward to lat. 20° N. (the larvae to lat. 23° 31' N.), from the Indian Ocean, and passing towards the Pacific to Djilolo Isl. (c. lat, 1° N., long. 127° 5' E.). The three, or perhaps four, next species are easily separated from 8. edwardsl, Kr., by several characters. On the ext. br. of urp. at least c. ^ of the exterior margin Is naked. In mxp.3 the sixth joint is divided Into but 4 subjoints very unequal In length, the third being but half as long as the second; the joint ends with but one spine, which is very long, and the interior margin of the joint is armed with but 15-25 spines, and no spine exists on the side of any of the subjoints near the exterior margin. J 62* |