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Show 1877.] MR. G. S. BRADY ON BRITISH FRESHWATER MITES. 27 Family ACARID^E. Genus SCHISTOSOMA, nov. gen.1 In general appearance resembling Sarcoptes; posterior portion of the body divided into two wide triangular processes; two hinder feet entirely different in structure from the anterior pairs, and projecting directly backwards from the back of the body, the anterior legs also arise from the truncate anterior margin of the body. SCHISTOSOMA LONGISETOSUM, nov. sp. (Plate III. fig. 1.) Body subquadrate, truncate in front; rostrum obtuse and prominent, posterior extremity divided into two triangular pointed laminae, each of which bears several terminal setae, one pair of which is excessively long; near the centre of each lamina is a circular organ, not unlike the caudal auditory organ of Mysis. The two anterior pairs of legs are short and robust, each bearing a few setae and one or two marginal spines. The terminal joints of the posterior legs are divided into several slender segments and are destitute of claws ; those of the third pair bear one very long and a few smaller setae; the anterior legs terminate apparently in delicate suctorial disks. Behind the rostrum arise, one on each side of the median line, two long setae which project first laterally and then forwards, reaching nearly to the extremities of the feet. Several pairs of somewhat shorter setae arise from the margins and central portion of the body. The animal is pale coloured; and the integument appears to be less dense and horny than in most aquatic Acari. No eyes were visible. Length ^0 of an inch. One specimen only of this remarkable species was noticed in a gathering of Entomostraca taken by Mr. Robertson in an old canal at Peterhead. EXPLANATION OF THE PLATES. PLATE III. Pig. 1. Schistosoma longisetosum, magnified. 2. Baphignathus spinifrons, magnified. 3. Tbe same. Eostrum, palp, and portion of front of carapace. a. Eostrum; c. Margin of anterior portion of carapace ; b. Palp. 4. Mandibles. 5. Extremity of a foot, with claws. P L A T E IV. Fig. 1. Bhyncholophus hispidus, magnified. 2. Extremity of palp. 3. Extremity of foot, with claws. 4. Pachygnathus nigrescens, magnified. 5. Extremity of foot, with claws. 1 t7X«£w, to split; awfia, body. |