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Show 954 DR. H. J. HANSEN ON CRUSTACEANS [Dec. 1, specimens, the one determined by Chun, the other by Ortmann, are referred by these authors to the same species. S. cornutus, Kr., and especially S. longlsplnus, Bate, present some affinity to S. edwordsl, Kr., and allied species, which becomes very evident by the fact that a short process is found on the outer side of the third joint of trl.1 and trl.2 Of S. inous, Fax., I have seen no specimens. A. b. fl. 1. Of S. robustus, Smith, S. japonlcus, Bate (S. mollis, Smith), and S. blsulcatus, Wood-Mas., I have seen no specimens. Of S. robustus we possess several stages of the Mastigopus, but having found none of them described I will omit discussing them in this paper. A. b. /3.2. This rich section of adults and larvae I have called the arctlcus-gvou.]), as they are very nearly related to each other, and S. arctlcus, Kr., is the only one well described of the mature forms and the sole species of which I am able to trace the whole development from the Acanthosoma (inch) to the adult. I will begin with some remarks on the adults and on a subadult species. 8. arctlcus, Kr., is well represented by Kroyer (p. 240, tab. iii. fig. 7, a-g; tab. v. fig. 16); later on S. I. Smith, in the various papers (see above), communicates some additional notes and good figures. The species has been captured in the Atlantic, northward to Greenland, and southward to lat. 38° S., long. 12° E. (Mus. Copenh.); further, in the Mediterranean near Ischia (8. magnlficus, Chun), and some older larvae in the Adriatic at Ragusa and Lesina (Chun's collection). But, together with these last larvae, I found in Chun's collection some young specimens and older larvae of a new and unfortunately closely related species, S. medlterra-neus, n. sp., which makes it necessary to present some remarks on the two species, so that it will be possible to distinguish them from each other. Previously no valid species allied to S. arcticus, Kr., was known from the Atlantic or the Mediterranean. The largest specimen of S. mediterraneus, in., is 19"5 m m . long, and has almost assumed the adult shape, but the eyes are still not black and therefore their final magnitude cannot be determined. Of characters between this subadult stage aud the subadult aud adult S. arcticus, Kr., I have found the following :-S. mediterraneus is destitute of the hepatic spines and the gastro-hepatic groove ; the supra-ocular spines are quite rudimentary ; the basal joint of the antenn. peduncle is obviously somewhat shorter than the two following taken together, which are a little more coarse than in S. arctlcus, while the basal joint from the spine near the basis of the exterior margin is somewhat more narrow, with the exterior margin less convex in outline than in S. arctlcus; the ext. br. of urp. is but 4 times longer than broad, with the outer margin beyond the spine strikingly concave. In S. arctlcus, Kr., the supra-ocular and hepatic spines and the gastro-hepatic groove are well developed; the basal joint of the antenn. ped. is (measured with accuracy) almost or quite as long as the two following taken together; the ext. br. of urp. is exactly 5 times longer than |