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Show 390 MR. F. E BEDDARD ON THE [Apf. 19, round the middle of the body, as in other Perichata, are much like those of other species on the hinder part of the body, that lying posterior to the clitellum; the setae of the anterior segments of the body agree very closely iu their shape with these, but are very much larger. On the clitellum, however, the setae are very different in appearance ; they are (woodcut, fig. 3) of very small size compared to the setae of the anterior preclitellar segments, and terminate in a distinctly bifid extremity; the two points in which the seta ends diverge at a considerable angle from each other, but are connected by a delicate membrane. The opposite extremity of the seta, which is imbedded in the body-wall, is abruptly truncated. The whole seta has not the 8-shaped curve which is so constant a character in the group, but is curved only in one direction. As in the other setae of the same species, and in the setae of Earthworms generally, the middle part is somewhat thicker; but this region does not lie in the middle of the setae but is closely approximated to the posterior extremity ; the part of the seta which lies behind the dilated region is straight. The general shape of these clitellar setae, apart, of course, from the bifid extremity, is like that of imperfectly developed ordinary setae. That this is not really the case with these setae is, however, clearly shown by the fact that all the setae of the several rows comprised in the clitellum have precisely the same shape, and also by the fact that in two specimens of the worm, which were the first that came to hand, the structure of these clitellar setae was precisely identical. This is, I believe, the first record of any such modification of the Fig. 3. i iifll Clitellar seta of Perichceta houlleti. clitellar setae in the genus Perichata. In P. affinis I have been to satisfy myself that the clitellar setae differ in no respect from the setae of the general body-surface ; in P. indica setae appear to be altogether wanting upon the segments of the clitellum. There are, however, other species of Lumbricidae in which there is a perfectly analogous modification of the setae ; in Lumbricus the clitellar setae are distinguished from those upon the other segments of the |