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Show 556 REV. T. R. R. STEBBING ON CRUSTACEANS [May 22, reminds us that the young of Porcellio have at first only six peraeon-segmeuts and six pairs of legs.1 It is rather provoking that he did not give fuller details, since in his account so far as it goes there are many points calculated to excite some surprise. The small size, the linear form, the anal filament, the heart-shaped caudal segment with uropods projecting to the rear, were little to be expected in the young of Sphceroma gigas. The truth appears to me to be that Guerin-Meneville was misled by the minute size and semi-pellucid hue of Iais pubescens (Dana) into supposing it to be the young of the Sphceroma, of which it is, so far as known, the invariable companion. W e now pass to the description of the adult Exosphceroma gigas. The short but broad vertex of the head is separated from the occiput by a nearly straight ridge, the front line of the vertex being indentured on either side of a short rostral point, its outer angles meeting the advanced points of the sides of the first peraeon-segment a little in front of the eyes. All the segments of the peraeon have the grooving described by Miers. The segments from the second to the seventh are almost parallel-sided, but the sixth and seventh slightly widen out. Again, the first division of the pleon is infinitesimally wider than the seventh segment of the peraeon. This first part of the pleon is composite, a continuous line near the base, and for the most part usually concealed under the peraeon, marking off the first segment, while from the broad second, the successively narrower third and fourth are marked off by lines which are interrupted at some distance from the middle. The second division probably consists of an obscure and concealed fifth segment, the sixth carrying the uropods and the telson. This division is so adjusted that in spirit-specimens the animal cannot be flattened out but has a crook in its back, which would appear to facilitate a doubling together of the body rather than the spherical form so readily assumed by Sphceroma serratum. The inflation of the caudal shield declines rather rapidly near the slightly sinuous sides and the rather narrow rounded apex. The eyes are dark, small, irregularly oval, near the posterolateral corners of the head. First antennae.-First joint large, broad, with basal fold, second much smaller, third longer but much narrower thau second; flagellum shorter than peduncle, 17-jointed, each joint except first and last carrying two hyaline filaments. Second antennae.-Longer than first, with stouter flagellum of about 16 short and stout joints. Epistome widening much downward. Upper lip with distal margin almost straight, except at the angles. Mandibles.-Cutting-edge tridentate, accessory plate stronger 1 M. Louis Roule, " Etudes sur le Developpement des Crustaces," Ann. Sci. Nat. ser. 7, vol. xviii. pp. 46, 57, 61 (1895), contravenes this long-accepted statement, though admitting the small comparative size of the seventh segment and its pair of appendages. |