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Show 668 MR. E. J. M I E R S O N A C O L L E C T I O N O F [June 19, joint of the uropoda in situ. One, which is loose in the tube, and almost certainly belongs to this species, is short, barely twice the length of the basal joint. As the external antennse are wanting, it must be a matter of uncertainty whether this species is to be referred to this genus or Oniscus. The Porcellio spinicornis and Porcellio nigra of Say (Journ. Ac Nat. Sci. Phil. i. pp. 431, 432, 1818), from the United States, belong to this subgenus, as specimens in the British-Museum collection presented by Say, prove. In both species the body is more closely articulated, and the terminal segment more triangular and shorter than in P. cayennensis. Subgenus PORCELLIONIDES. Postero-lateral angles of the first four segments of the body not acute and not produced backward. a. Depressed, with the antero-lateral portion of the head small. PORCELLIO JELSKII, sp. n. (Plate LXVIII. fig. 3.) Oblong-oval, depressed, very finely and closely punctulated, and with scattered but faintly indicated granules, tending to a transverse arrangement on each segment. Head small, transverse ; anterolateral lobes very small, nearly obsolete. Eyes small, black. First four segments of the body with the posterior margins straight, and forming nearly a right angle with the lateral margins ; remaining segments with the posterior margins becoming successively slightly more excavated and with the postero-lateral angles subacute. Tail short; third to fifth segments with the posterior margins straight to within a short distanee of the postero-lateral angle, which is acute, and directed backwards ; terminal segment triangular, rather broader than long, with a slight depression above, with the lateral margins a little excavated, subacute at the extremity, and projecting but verv slightly beyond the basal joint of the uropoda. Antennse slender, with the two terminal joints (flagellum) together about as long as the preceding, the terminal a very little shorter than the penultimate joint. Uropoda with the terminal joint two or three times as long as the preceding, narrow-lanceolate, acute at the extremity. Colour light purplish-brown, variegated with irregular narrow pale markings ; lateral margins of the segments without broad yellow bands. Length 5 lines, breadth 2 lines. Hab. Peru; Guiana. A large series of sp?cimens of this species, which appears to be common, is in the collection. This species differs from P. chilensis, Dana (nee Gay), in the joints of the flagellum of the external antennse (in that species the first is nearly twice the length of the second joint), the more deeply concave seventh segment of the body, and the longer rami of the uropoda-from P. cubensis and P. sumichrasti, De Saussure, from Cuba (which it somewhat resembles in the form of the terminal |