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Show 660 MR. E. J. MIERS ON A COLLECTION OF [Julie 19, teeth of the rostrum are variable in number in different examples the same species ; and even the comparative length of the joints of the second pair of legs (which affords excellent specific characters when taken from adult animals) is less trustworthy in younger specimens. After having examined a considerable number of species of this genus, I may express m y belief that some of them-perhaps some even of those included in the present paper-will, upon comparison of larger series of specimens than we at present possess, be found to represent merely different stages of growth of the same animal. Dr. von Martens, in two papers in the Archiv f Naturgeschichte, xxxiv. p. 34 (1868), and xxxv. p. 32 (1869), has done good service toward elucidating this difficult genus by exhibiting in a tabulated form the diagnostic characters of the species inhabiting the Eastern-Asiatic Region, and South Brazil. PALCEMON NATTERERI. Palcemon nattereri, Heller, Kais. Akad. Wissensch. Sitzungsber. xiv. Abtb. i. p. 414, pl. ii. fig. 36, 37 (1862) ; von Martens, Archiv f. Naturg. xxxv. p. 32 (1869). Hab. Guiana (river St. Laurent) (Jelski). This species was described by Heller from specimens collected by Natterer in the Rio Negro, Brazil. It is distinguished from its congeners from the American continent by the elongated, strong, second pair of legs, which are closely spinulose, and of rather unequal size ; the palm is much longer than the wrist; the upper (mobile) finger has two, the lower a single strong tooth on its inner margin. The sides of the carapace below the hepatic spine are very rough and scabrous to the touch. Two specimens are in the collection, which I refer to this species : in the larger (length to anterior margin of carapace 2 inches) the rostrum is imperfect; in the smaller the rostrum J^*- is toothed. In the smaller specimens; as is always the case in the species of the genus Palcemon, the distinctive characters are far less strongly marked. PALCEMON BRASILIENSIS. Palcemon brasiliensis, Heller, Kais. Akad. Wissensch. Silzungsb. xiv. Abth. i. p, 419, pl. ii. fig. 46 (1862); von Martens, Archiv f. Naturg. xxxv. p. 32 (1869). Hab. Guiana (R. St. Laurent) (Jelski). Three specimens of this species are in the collection; the length of the largest is 1 inch 10 lines to tip of rostrum. Two specimens agree well with the figure and description of Dr. Heller, whose specimens were collected by Natterer in a brook at Camaroes, in Brazil. It is to be noted, however, that the second pair of legs, which he describes as unequal, are, in the specimens from Guiana, very nearly of equal length. This species was found in the same stream with the preceding. The legs are not so robust, and more minutely spinulose, the palm |