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Show 1896.] OF THE GENUS SERGESTES. 957 the Atlantic (inch the Mediterranean and tbe Arctic sea at Greenland). This is of importance for the reference of larval stages, as Bate has established the species :-S. dorsosplnalls, Bate (p. 394, pl. lxxii. fig. 1) and S. laterodentatus, Bate (p. 395), captured "associated with" another "South of Australia"; 8. nasldentatus, Bate (p. 398, pl. lxxii. fig. 2), " between Valparaiso and Juan Fernandez"; S. rlnkll, Bate, vix Kroyer (p. 404, pl. lxxiii. fig. 3), " N e w Hebrides " and " South Pacific " ; and S. Icevlventrails, Bate (p. 425, pl. lxvii. fig. 3), " North of N e w Guinea"--which 5 reputed species are all larvae and all belong to two or three species closely related to 8. arctlcus, Kr., or perhaps partially belong to that species. But Bate's representations are not sufficiently good for the decision of such questions : thus, f. inst., the chances are that he has overlooked tbe hepatic spine in some of the " species," while S. laterodentatus, Bate, has obviously been established on a specimen with a long hepatic spine, which has given rise to the name. His description of S. rlnkll either involves the fault that the rostrum, which is described and figured as short, has been broken off, or the form must decidedly be different from 8. rlnkil, Kr., as a short rostrum and dorsal abdominal spines are not coexistent in this latter species.-In all probability Bate's 5 species belong to two or three of the other known species of the arcticus-group, and none of them to S. arcticus, Kr., itself. Further elucidation of the adults and the larvae of the arcticus-group I am not able to derive from existing literature. Yet the result has been that 2 adult and 2 larval species have been cancelled as belonging to S. arcticus, Kr., and the other related forms ; 3 adult species and 4-5 larvae have been collocated into the group ; finally one new species has been established. B. S. comiculum, Kr.-The stage described and figured by Kroyer (p. 252, tab. iii. fig. 4, a-e) and Bate (p. 410, pl. lxxv. fig. 1) is a half-grown larva. The mature form is unknown. The adult with black eyes, 20-22 m m . long, is rather remarkable, as the body is extraordinarily slender, wdth a considerable distance between the mouth and the eyes, thus in that respect approaching to S. tenulremls, Kr., and being intermediate between this species and f. inst. S. arcticus, Kr. Its rostrum is a little lower thau in 8. arctlcus, Kr., the supraocular spine rudimentary or lacking, the hepatic spine short, the gastro-hepatic groove distinct. The eyes are but a little broader than the end of the stalk; in the long antenn. ped. the first joint is considerably longer than the third and this considerably longer than the second. An interesting character is that the sixth joint of mxp.3 is divided into 4 sub-joints, the distal three of equal length and the first somewhat longer, and each of these 4 joints is more or less distinctly divided into 2 joints : thus we obtain 8 sub-joints, of which 7 possess a long seta or slender spine on each side near the apex, but the two spines are not placed opposite to each other, and the last sub-joint has a pair of slender apical spines. The branchiae recall those in S. arctlcus, Kr.: above trl.3 two branchiae, the first long, the second several |
