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Show 1896.] OF THE GENUS SERGESTES. 959 vii. Notes on the Species In Group II. A. S. henseni (Ortm.).-Of this interesting species I have seen only two adult specimens, lent me by Geheimrath Prof. Dr. V. Hensen. As the representation by Ortmann (p. 38, Taf. iii. fig. 3) is rather deficient, I shall add some notes. The rostrum is low and short; the supraorbital and hepatic spines are short. Mxp.3 is considerably longer than trl.3 and its 4 proximal joints, though more slender than in the following species, are yet much stouter than in trl.3; the 2 distal joints are quite naked along one margin, the fifth almost more than double as long as the sixth, which is divided into 5 subjoints, the last 4 of which are equal in length, while the first of them is as long as the two following together; at the base of the first subjoint and at the apex of the first, third, and fifth subjoints is found a long spine; at the apex of the second, fourth, and fifth subjoints a spine about half as long as the long spines ; finally along tbe same margin a fine comb of very numerous spines about as long as the diameter of the joints ; the fifth joint of mxp.3 has about 10 longer spines along the margin and on its distal two-fifths a comb similar to that on the sixth joint, but its spines become shorter towards the base. By this singular armature the species is easily distinguished from all other species known to me. Above trl.3 a large and a very small branchia, the latter of which is less than a third as long and but half as broad as the large branchia; above trl.4 two branchiae, the anterior somewhat larger, the posterior somewhat smaller than the small branchia above trl.3; thus the branchiae are very different from those in the other species of the group. In the following species we find a well-developed process on the third joint of trl.1 and a similar one on trl.2, but iu this species the process in trl.1 is rudimentary and wanting in trl.2 On the ext. br. of urp. no spine is found on the exterior margin, and in the one specimen the ciliated part occupies three-fifths, in the other specimen almost four-fifths of its length. In no other species have I met with any similar variation in this feature, but it also exists in the larvae (see below). S. sargassi, Ortmann (p. 34, Taf. iii. fig. 1), is the Mastigopus of S. henseni. As the material seen by m e is rather incomplete, the larger specimens being not very large and besides defective, I add only a few remarks to Ortmann's description. Mxp.3 is elongated and incrassated in proportion to the legs as in the adult, the fourth joint at the apex and just above the articulation produced into a large, conical process-a very good character for the species ; and in a larva a little more than half-grown the sixth joint was already divided into the 5 subjoints. In the largest well-preserved specimen, 8 m m . long, I found above trl.3 a large branchia and a lamella, comparatively somewhat larger than usual, which had begun to develop itself into a very small branchia, above trl.4 a very small branchia and a simple lamella; tbe normal lamellae above trl.1 and trl.' are a little larger than usual. As in the adult the ciliated pare on the exterior margin of the ext. br. of urp. occupies about three-fifths or four-fifths of its length in specimens between 4'5 m m . and PROC ZOOL. Soc-1896, No. LXII. 62 |
