There are always six pairs; each biramous and multiarticulated, supported on a pedicel formed of two segments. A shield-like swelling at the exterior bases of these pedicels often appears like another segment; but such, I believe, is not its nature. The five posterior pairs answer to the five pairs of ambulatory legs in the higher Crustaceans; and as in the case of the latter, the three, or the four hindermost pairs almost invariably resemble each other. The first pair, which is homologous with the outer maxillipeds of ordinary Crustaceans, is separated by an interval from the second pair;--though this is not the case with the legs of the pupa, from which the cirri are metamorphosed. These anterior cirri are attached to the lateral edges of the mouth, namely to the thickened rim of membrane, forming the supposed basal segment of the mandibles. They are capable of more diversified movements than the other cirri: the anterior ramus is always elongated, with the terminal segments more or less tapering, and is directed beyond (or anteriorly to) the mouth: the shorter ramus closely resembles in structure the rami of the second pair. In the Chthamalinæ the second pair, and in the Balaninæ the second and third pairs (as will be more particularly described under these sub-families) differ in structure from the posterior pairs, from which they are separated by a slight interval. The number of segments on the posterior cirri is often great, amounting in Chelonobia even to fifty. Each segment normally is furnished on its inner face, which is usually somewhat protuberant, with from two to rarely eight or ten pairs of long spines or bristles, placed in a double row; the two spines in the lower pairs stand nearer to each other, and are shorter than the spines in the upper pairs. Between each pair of spines there is either a single, very thin bristle, or often a tuft of such. The pairs are directed somewhat upwards, and they diverge when the cirri are uncurled; their function is obviously to entangle the prey. On the dorsal or exterior surface of each segment, close to its upper margin, there is a tuft of spines, often composed of thicker and thinner spines; these, I believe, serve to prevent any creature intruding within the sack. On both sides of the upper margin of each segment, there is generally a row of short, blunt, excessively minute spines, which only deserve notice, inasmuch as it is by their increase in number and size, and by the spreading out of the dorsal tufts, and, lastly, by the increase of the little tuft intermediate between the pairs of spines situated in front, that the segments on the two or three anterior pairs of cirri become covered, like brushes, with bristles. The bristles or spines on the second and third cirri are often, especially in Tetraclita, doubly and coarsely pectinated. The bristles on the pedicels follow the same arrangement as on the rami; namely, being in regular pairs on the posterior cirri, and crowded