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Show 138 DR. W. B. BENHAM ON [Feb. 16, belongs to Perrier's genus, and name it after that zoologist. I shall reserve certain histological points for later consideration. PLUTELLUS PERRIERI, n. sp. It has a length of 2 inches (50 mm.) and a comparatively great diameter-namely a little more than •!• inch (4 m m . ) ; the length of the clitellum is 4 mm., and the distance from its anterior margin to the tip of the prostomium is 7 mm.1 There are 126 somites in the specimen which remains uninjured ; they are all well marked and are only obscurely annulated. The two extremities of the worm are rounded, obtuse, and not noticeably attenuated, and at the posterior extremity the body is slightly dilated. The prostomium is distinct and completely dovetailed into the buccal somite, as it is in P. heteroporus. The clitellum, when the worm is fully developed, extends all round the somites xiii. to xviii., with the exception of the median ventral region of the last somite and a short portion of the first somite. The intersegmental grooves are entirely obliterated and the anterior and posterior boundaries are very sharply defined. In the specimen dissected, where the clitellum was not so fully developed, the ventral surface of the somites was less glandular and the grooves less obliterated than in the entire specimen, and a pair of papillae exist on somite xviii. between the chaetae " 1" and " 2." In the fully matured form, the glandular modification of this somite extends ventrally so as to become continuous with these papillae, which are then no longer evident. [In P. heteroporus the clitellum is also complete, occupying somites xiv. to xvii., but overlapping the anterior part of somite xviii.] The chcetce, eight in number, are isolated ; the ventralmost-constituting the series of chaetae " 1"-on each side is close to the middle line ; if the space between " 1" and " 2 " be taken as the unit, represented by S, the space between the ventral chaetae of the two sides is 2S, that between the second and third is l±S, that between " 3 " and " 4 " is 2S, and the dorsal area, between the dorsalmost chaetse of the two sides, is 5S; the chaetae " 4 " lie dorsally (Plate VII. figs. 2 and 4). Posteriorly the space " 1-2 " is slightly greater than it is anteriorly; and anteriorly to the clitellum, space 1-1 is less than it is posteriorly. [In P. heteroporus the chaetae are equidistant, but posteriorly the dorsal and ventral spaces are a little greater than the lateral spaces, and spaces 1-2 aud 3-4 are a little less than anteriorly.] The chaetae themselves are of the usual lumbricid form, without ornamentations; there are no modified, copulatory chsetaa of any sort. The nephridiopores are not visible externally in m y specimens, which are very well preserved, and the segments probably a good deal closer together than in life; but I find from m y longitudinal sections that they have the following arrangement (Plate VII. figs. 2 & 4) :-The first pore lies on the anterior margin of somite hi., and, 1 These figures for P. heteroporus are 15 cm. as length of body, 6 mm. as length of clitellum, and 4 mm. as its distance from the extremity of the body. |