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Show 708 MR. W. T. CALMAN ON MACRUROCS [May 16, In G. wyckii * and G. typus I find the following arrangement:- Pleurobranchiae Arthrobranchiae Podobranchiae mxp.2 1 mxp.3 21* ep. per1. 1 1 ep. per.2 1 ep. per.3 1 ep. per.4 1 ep. per.5 1 This agrees with the formula for Atya. Claus states that Troglocaris lacks the arthrobranch of the first peraeopod. According to Boas, Atyaephyra desmarestii has no arthrobranch on the first peraeopod, and only one on the third maxilliped. The males are usually somewhat smaller than the females, and have as usual the pleural plates of the abdomen less deep. In the female the two flagella of the antennule are of about equal length, and about twice as long as the peduncle, the outer flagelluin being slightly thickened for about two-thirds of its length. In the male both flagella are much elongated, the outer being longer than the inner, and in uninjured specimens measuring more than four times the length of the peduncle, or about one-half the length of the body. The thickened basal part is more distinct than in the female. I have not observed any sexual differences in the armature of the walking-legs or of the maxillipeds, nor in the shape of the anterior margin of the carapace, such as are described by Muller in Atyoida. The eggs carried by the females are ovoid in form, measuring about 4 8 x *27 m m. Total length of largest specimen ( 5 ), 23 m m. Many specimens of this form were collected in shallow water. Comparing the new form with the other genera of Atyidce as revised by Ortmann (Proc. Acad. Nat. 8c. Philad. 1894, p. 397), we find that (like all the other higher Atyidce) it differs from Xipho-caris, Troglocaris, and Atyaephyra in the absence of exopods from all the peraeopods. It resembles Caridina and differs from Atya and Atyoida in the fact that the carpus of the second peraeopods * The formula given by Hickson is incomplete (Ann. Mag. Nat. Hist. (6) ii. 1888, p. 361). Although the number of the epipods (mastigobranchiae) is given correctly, these organs appear to have escaped his notice, for he figures as " mastigobranchias" the long coxal seta; of the peraeopods. The true epipods are of a shape similar to those of many other Caridea, and like those figured by Joly in Atyaephyra and by Miiller in Atyoida, consisting of a short curved stem directed backward and terminated by a strong hook which grasps firmly the coxal setas of the next suceerling peraeopod. t It is possible that one of these should be regarded as a pleurobranch. In Atya the corresponding gills are certainly arthrobrauchs, as stated by Pocock (A. M . N. H . (6) iii. 1889, p. 15). Claus, who does not attach much morphological importance to the place of insertion, assigns these two gills to his series b & c respectively (Neue Beitr. z. Morph. d. Crust., Arb. Zool. Inst Wien, vi. 1884, p. 57). |