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Show 1896.] OF THE GENUS SERGESTES. 951 To this group further belong *S.hamlfer, Ale. & And., which I am not able to recognize, and the following larvae : S. Intermedins^ Bate, S. dlapontlus, Bate, S. fermerlnkil, Bate, S. splnl-ventralls, Bate, and S. ventridentatus, Bate, several of which certainly belong to some of the species in the tabular view, but I cannot recognize them; S. monophthalmus, Stimps., in all probability being a younger S. vlgllax, Stimps.; finally S. hrachyorrhos, Kr., which is a very young larva of S. edwardsil, Kr. (see later on). S. arachnlpodus, de Nat., and S. profundus, Bate, I have not been able to refer to any one of the groups ; to Petalldlum is transferred S. obesus, Kr. (S. sanguineus, Chun), and excluded as not belonging to the genus are 8. serrulatus, Kr., and S. caudatus, Kr. vi. Notes on the Species of Group I. A. a. S. tenulremis, Kr. The specimen described by Kroyer (p. 255, tab. iv. fig. 11, cc-b) is a hardly half-grown Mastigopus; S. longicollus, Bate (p. 421, pl. lxxvii. fig. 1), is almost (or perhaps fully) adult; S. junceus, Bate (p. 416, pl. lxxvi. fig. 1), is the young Mastigopus, 6 m m . long, with dorsal spines on the 4th- 6th abdominal segments. I have examined a specimen 23 m m . in length, which had just obtained the black eyes ; the species grows at least somewhat longer before maturity, but the mature form is unknown. The obtaining of black eyes does not always take place at the same length of the animal, as a specimen with the larger, oblique, yellowish eyes is even 26 m m . long. The species is easily separated from all other known forms by the combination of two characters : the very long and slender body with the long distance between the eye-stalks and the mouth-organs, and the ciliated parts on the ext. br. of urp. occupying, in the older forms scarcely 5, in the younger a little more than -*- of the exterior margin. The quoted figure of S. longicollus, Bate (pl. lxxvii.), gives a tolerably correct notion of the species. It may further be added that of the two branchiae above trl.3 the first is long and the second a little more than half the length of the first and but a little shorter than the first branchia to trl.1, while the second above trl.4 is somewhat smaller, but still very well developed. I have seen specimens of this species from numerous localities in the Atlantic, northward to lat. 32° 16' N., in the Indian Ocean, and in the Pacific as far as the Matelota Islands and lat. 16° 8' S., long. 111° 50' E. A. b. a. S. atlanticus, M.-Edw. As to the synonymy etc., see above. The best representation of this very common species is given by Krciyer (S. frisll, Kr., p. 235, tab. i. fig. l,a-v). The sixth joint of mxp.3 consists of 6 subjoints, the 4 distal of equal length and each of the 2 proximal as long as 2 of the distal subjoints together. The branchial formula as in S. japonlcus, Bate (8. mollis, Smith), viz. a podobranchia and a lamella to mxp.2, a pleurobranchia and a lamella to mxp.3 and trl^-trl.', finally 2 pleurobranchiae to trl.4, but the branchiae are longer than in S. mollis, Smith (Rep. Comm. Fish and Fisheries f. 1885, pl. xx. fig. 5), and |