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Show 1868.] MR. C. SPENCE BATE ON NEW FRESHWATER PRAWNS. 363 4. On a new Genus, with four new Species, of Freshwater Prawns. B y C. S P E N C E B A T E , F.R.S. (Plates XXX. & XXXI.) MACROBRACHIUM, gen. nov. Carapace armed anteriorly with a vertically projecting rostrum. Eyes with short peduncles, not concealed beneath the carapace. Superior antennse having the first joint of the peduncle caved upon the upper surface ; second and third joints cylindrical. Flagella three-branched, the smallest branch united to the largest. Inferior antennae furnished with a large scale; flagellum long and slender. Mandibles having a molar and an incisive process, and furnished with a triarticular appendage. Gnathopoda pediform. First pair of pereiopoda slender, about as long as the carapace, didactyle; second pair immensely developed (in the male), longer than the entire length of the animal from the extremity of the rostrum to that of the telson. Posterior three pairs simple, robust. Posterior pair of pleopoda longer than the telson. Telson triangular, terminating in a single point. MACROBRACHIUM AMERICANUM, sp. nov. (Plate XXX.) Carapace nearly half the length of the animal. Rostrum short, armed above with eleven anteriorly projecting dental processes, of which the last four are posterior to the orbital margin of the carapace, and furnished with short, stiff hairs in the depressions between the teeth ; below with three simple teeth. The rostrum has the anterior portion depressed, the apex being slightly elevated. Behind the margin, at the lower extremity of the orbit, is a single, sharply pointed tooth, behind and below which is a sharp spine or tooth that is surrounded at the base by a suture that passes from it on the anterior side to the anterior margin of the carapace. Pleon deep, scarcely longer than the carapace. Eyes globular. Superior antennae having the peduncle scarcely longer than the rostrum ; first joint half the length of the peduncle, inner surface flat, perpendicular, furnished with a single tooth near the centre of the lower edge, superior surface concave (for the lodgment of the eye); outer margin thinned out to a fine edge, furnished with a sharp, anteriorly directed tooth near the centre, and another at the distal extremity; the next two joints are short. The smallest flagellum united to the largest for about one-fourth of /in inch from the base. Inferior antennae having the peduncle about half the length of the superior. The large squamiform process nearly half as long again as the rostrum, furnished with an external subapical tooth. Flagellum about as long as the second pair |