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Show 1896.] OF THE GENUS SERGESTES. 953 which, from the spina on the outer margin, is strongly taperino-towards the apex, the outer margin even being slightly concave in outline; the sixth joint of mxp.3 is distinctly 4-jointed, the relative length of these subjoints as in the larva (see below). Above trl.3 a well-developed pleurobranchia and a lamella, above trl.4 a well-developed pleurobranchia and a lamella with 2-5 branches at the tip, thus a branchia very little developed and more feeble than in any other adult species known to me. 8. longlsplnus, Bate (p. 417, pl. lxxvi. fig. 2), is most decidedly the larva of S. cornutus, Kr. It attains a length astonishing as compared with that of the adult. The specimen which I am about to describe is 13 m m . long, while the adult male is but 16 m m . The rostrum is somewhat longer than in the adult, without dorsal spine, the supra-ocular and the hepatic spines and the gastro-hepatic groove are well developed. The eye-stalks are very long, the large, somewhat oblique eyes lie above the basis of the third joint of the antenn. ped., the relative length of which is almost as in the adult. Mxp.3 is but little longer than trl.3 and constitutes in several respects a transition-form to S. edwardsl, Kr., and allied species ; the first joint is considerably incrassated, second-fourth joints but little coarser thau in trl.3, the fourth joint with very few and short bristles, the fifth with few setae more developed on the one than on the other margin, the sixth joint as long as the fifth (a character also found in S. atlanticus, etc., while in the edwardsi-growp the fifth joint is much longer than the sixth), divided into 4 subjoints, of which the first is f times longer than the second, and this is as long as the last 2 subjoints together, which are about equal in length, or the third somewhat longer than the fourth ; the 3 proximal subjoints each with very few short setae, and at the end with 2 very long stiff setae or slender spines, the fourth subjoint with one short and 3 very long apical spines, which, however, are scarcely more robust than those on trl.2 or trl.3, trl.4 reaching a little beyond | of the fourth joint of trl.3 Above trl.4 a well-developed branchia and a lamella with 3 short apical branches. The 3 anterior abdominal segments each with a rather short dorsal spine, which, at least on the 2 anterior segments, is directed obliquely forward, the fourth segment without any spine and the fifth and sixth each with a short spine; the 4 anterior segments having on the middle of each epimeron a spine directed outwards, the spine being short on the three segments and somewhat longer on the fourth, the fifth segment with a very long spine directed downwards and bending somewhat forwards, and issuing from the inferior margin at a short distance from its posterior end; tbe sixth segment with a small spine turned downwards from the posterior edge. As in the mature form, the ciliated part occupies between 4- and | of the exterior margin of the ext. br. of urp. The specimen described differs considerably from the figure given by Bate, but the form described by him is somewhat younger. M y determination is decidedly correct, as two similar |
