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Show 614 MR. J. DOUGLAS-OGILBY ON [Dec. 6, or a child with the proportions of a full-sized adult. All these distinctions therefore, instead of indicating diversity, are rather conclusive evidence of affinity, unless size itself is to be considered as a worthy ground of generic distinction. After all a generic name is purely a matter of convenience, aud for m y part I think it more desirable and instructive to call the Liberian species Hippopotamus, and thereby to indicate its close relationship with the well-known large animal of that name, than to give it a designation in which this affinity is lost sight of. It m ay be sometimes expedient to divide up genera in which the number of species are excessive upon comparatively trivial characters; but in the case of Hippopotamus, with only two living and but few extinct species, no such reason can be alleged. 4. On a new Genus and Species of Australian Mugilidse. By J. D O U G L A S - O G I L B Y , Department of Fishes, Austr. Mus. Sydney. (Communicated by F. D A Y , C.I.E., F.Z.S.) [Received November 1, 1887.] TRACHYSTOMA, gen. nov. Branchiostegals six ; pseudobranchise present. No adipose eyelids. Vomer and palate furnished with distinct bands of villiform teeth ; jaws toothless. Scales rather small, finely ctenoid. TRACHYSTOMA MULTIDENS, sp. nov. B. vi. D. 4i. A. 3/9. V. 1/5. P. 15. C. 14. L. lat. 48-51. L. tr. 16. Length of head 5j to 5^, of caudal fin 4 | to 5j, height of body 41 to 5 in the total length. Eye without adipose lids, the diameter of each 4\ to 4 3 in the length of the head, li to lj diameters from the end of the snout, and 1^ diameters apart. Interorbital space convex; snout broad and depressed; upper lip not thickened. Angle made by the anterior edges of the mandibles moderately obtuse; the length of one of the mandibular rami is §-, or slightly more, of the width of the gape of the mouth. The maxilla reaches backwards to the vertical from the hinder margin of the posterior nostril. Preorbital serrated along its outer edge. Nostrils nearer to the eye than to the end of the snout; the anterior nearly circular, small; the posterior oval, large, about five times the size of the anterior. The free space on the chin is of moderate size and lanceolate. Teeth : a patch of villiform teeth on the vomer, sometimes crescentic, sometimes biclavate; palate with an elongate band, broadest anteriorly. Fins-. Spinous dorsal commences rather nearer to the base of the caudal than to the tip of the snout; its spines are strong, the first the longest, about two thirds of the length of the head ; the interspace between the two dorsal fins is rather less than the base of the spinous dorsal, while the distance between the origins of the two dorsals exactly equals the length of the head, |