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Show 1886.] DURING THE VOYAGE OF H.M.S. 'CHALLENGER.' 101 extreme lateral margin ; eyes are absent. The thoracic segments are separated by deep incisions ; the first segment is much the largest, and is fused mesially with the following segment; the margins of the segments are rounded ; and the whole body is fringed with numerous leaf-like flattened spines. 1. NEASELLUS KERGUELENENSIS, F. E. B., loc. cit. The extreme length of the single individual of this species is 2 millim. The body is extremely flattened and depressed, pear-shaped in general outline, being much broader anteriorly than posteriorly. The head is immensely extended laterally, being as wide as the following segment of the thorax, from which, however, it is separated by deep lateral incisions. The central region is convex ; the anterior and lateral margins are fringed with peculiar flattened spines, which also border the body throughout. The two first segments of the thorax are together about equal in length to the head in its middle region ; the line of suture separating these two segments is obliterated except laterally ; the remaining segments are short and subequal, each is about i of the length of the conjoined anterior segments ; the third, fifth, and sixth segments have lateral processes, fringed with the peculiar spines referred to, which are absent from the fourth and seventh segments. The shape of the abdominal shield, which is, as in Pleurogonium & c , separated from the last segment of the thorax by a single free abdominal segment, is rhomboidal; it is notched posteriorly and laterally where the uropoda articulate. The antennules and antennae arise from the extreme lateral margin of the head ; in the antennules the basal joint is short and stout, the second rather elongated, the third and fourth narrower and shorter than the second, the flagellum has two joints. The antennae are more than half the length of the body, the peduncle has six joints, the flagellum is a little longer than the distal joint. The mandibles are furnished with a palp. The first thoracic appendages are cheliform, the remaining thoracic appendages are not greatly elongate. The uropoda are as in Pleurogonium. Kerguelen, Christmas Harbour, 120 fathoms. Genus PLEUROGONIUM, Sars. 1. P L E U R O G O N I U M ALBIDUM, n. sp. This species is represented by a single female example measuring 3 millim. The general shape of the body is like the other species described by Sars ; the epimera of the first four thoracic segments are prolonged into spines, which are of equal size upon all the segments; the three posterior segments of the thorax are separated 1'rom each other and from the fourth by deep lateral incisions ; their epimera are prolonged into stout spiny processes, which are shorter than in the anterior segments; the dorsal surface of each of these three segments is traversed by a narrow ridge. Between the |