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Show 966 DR. H. J. HANSEN ON CRUSTACEANS [Dec. 1, That the referring of this Mastigopus to the above-described adult S. Incertus, n. sp., is correct is proved by a specimen c. 17 m m . long, which constitutes au excellent transition. The rostrum has still essentially the larval shape, with a sharp angle as the trace of the dorsal spine between the oblique basal and the horizontal distal part, but the distal part is shorter than the basal and its upper margin concave as in the true Mastigopus. The eyes about as in the adult, but still brown, not black, the eye-stalks as in the adult. The sixth joint of mxp.3 essentially as in the adult, with 13 spines on the interior margin. The abdominal segments are dorsally smooth. On the ext. br. of urp. the ciliated part occupies scarcely more than § of the exterior margin, and the spine is short. S. armatus, Kr.-Kroyer's representation (p. 260, tab. iii. fig. 6, a-e) gives a good notion of this curious larva. Here I shall but mention some few essential characters. The rostrum is about as long as or a little shorter than the first joint in the antenn. ped., without any dorsal spine or angle. The eye-stalks are of medium length, considerably shorter than in the larvae of S. Incertus, m., and S. penerlnkl, Bate. In the antenn. ped. the first joint is in the older specimens obviously somewhat shorter than the third. Of the abdominal segments the second is dorsally armed with a shorter perpendicular spine, the third to fifth wdth very long oblique spines, much longer than in other species of the group, and, besides, the spines on the fourth and fifth segments are much curved. Sometimes a very short spine is present on the first segment, and finally iu the younger specimens a short spine on the sixth. On the ext. br. of urp. the ciliated part occupies a little less than | of the exterior margin, and the spine is well developed. The largest specimen is 15-5 m m . long. That this Mastigopus does not belong to S. incertus, m., with which it agrees in the ext. br. of urp., is decided by the shortness of tbe first joint in the antenn. ped. in proportion to the third. Thus the adult form is unknown to me. Unfortunately all the specimens seen by me were captured in the Atlantic between lat. 42° 5' N. and lat. 4° 5' N., but Bate describes and figures (p. 401, pl. lxxiii: fig. 1) a specimen, 8 m m . long, which seems to be the same species, and the specimens seen by him were captured at " Port Jackson (Australia)," " north of the Sandwich Islands," and " between Japan and Honolulu:" thus it may be possible that it belongs to S. halia, Fax., captured in lat, 7° 6' N., long. 79° 48' W . Of the 8 species enumerated at the end of the tabular view as belonging to Group II., S. hamifer, Ale. & And., S. macrophthalmus, Stimps., and S. brachgorrhos, Kr., are mentioned in the notes. The other 5 species are all larvae. S. diapontlus, Bate (p. 399, pl. lxxii. fig. 3), is very interesting, being 18 m m . long and easily distinguished from all other species of the group by having the second joint of the antenn. ped. " twice as long as the first;" this large larva, captured in the Atlantic, must belong to an unknown adult form-thus we obtain at least 7 valid species (S. hamifer, And. & |