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Show 758 PROF. T. H. HUXLEY ON THE CLASSIFICATION [June 4, truncated anterior end with the coxopodite of one or other of the thoracic limbs, from the second maxillipede to the penultimate ambulatory limb inclusively. I shall therefore term these gills podo-branchiee. A fold of the integument rises over the outer face of the basal portion of the branchia, which is freely movable, inwards and outwards, upon its articulation. The basal portion of the branchia curves slightly upwards, and is continued into the comparatively narrow stem (fig. 1, st), which bends up at right angles to the base, and lies nearly parallel with the inner wall of the branchial chamber. Rather beyond the middle of its length, the stem expands into the broad lamina (fig. 1, I), the two lobes of which are folded together like the leaves of a partly open book, their free rounded edges being turned backwards and the uniting fold forwards. The lamina of each branchia, from the second to the sixth, is received between the lobes of the lamina of that which precedes it, and, from the first to the fifth, receives the lamina of the branchia which follows it. The edges of the laminae are beset with minute hooked spines, seated upon low tubercles (fig. 1, iv.), and are flat; but, a short distance within the edge, each lamina is folded longitudinally in such a manner as to give rise to ten or twelve plaits. From the mode of their formation, these plaits or folds are, of course, as distinctly marked on the outer as on the inner faces of the laminae (fig. 1, in.). Small elevations, terminated by minute hooked setae, like those on the edges of the laminae, are observable on both faces, particularly on the ridges. The inner lobe of the lamina is continued down the stem as a decurrent gradually narrowing fringe, which terminates ou the inner face of the basal portion (fig. 1, n. g). The outer lobe ends more abruptly, in a thin ridge which lies external and posterior to the last. Between this ridge and the fringe there is a longitudinal groove, which occupies the inner and posterior face of the stem. A short distance from the upper edge of the lamina, and proceeding, as it were, from the anterior face of the median fold of the latter, the apical plume (fig. 1, i. a p) is given off. At its base this is beset with cylindrical branchial filaments; but at its free extremity it becomes simple and filiform ; at its attached extremity, it passes into the stem of the gill, of which it is seen to be the direct continuation. The whole of the outer aud anterior face of the stem, as far as the basal fold, is beset with branchial filaments, of which those in the region of tbe lamina are the longest, while towards the base they are shorter and more closely set. Close to the attachment of the podobranchia, the upper surface of the coxopodite presents a rounded elevation, from which a great number of long, flexible and tortuous setae proceed (fig. 1, vi.). When undisturbed, they ascend vertically between the gills on the sides of the branchial chamber. The apex of each of these coxopo-ditic setce is acute ; and at a short distance from its extremity it is beset with numerous short foliaceous scales, which gives it the aspect of a minute catkin (fig. 1, vu.). Further down these scales become |