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Show 1892.] OF THE GENUS PERICH.ETA. 169 In b there are three pairs of spermathecae in segments vi., vii., viii., which are in every respect perfectly normal. In c there are two pairs lying in vi. and vii., but quite normal in structure. It may be that I am wrong in associating all these individuals together under one specific name. PERICHCETA HESPERIDUM, n. sp. Two individuals out of the five specimens just referred to, of which I have described three under the name of Perichceta barbadensis, presented certain differences; these differences would, if the specimens had come from a different locality, be undoubtedly considered of specific value. As it is, I am uncertain, considering their exceedingly close similarity in coloration, whether to regard all five individuals as belonging to one protean species, or whether to regard the two specimens described here as a distinct species. Since the differences which they show to the three described as Perichceta barbadensis are more marked than either of the three exhibit amon0, themselves, I give them at least a provisional name. The external characters are those of Perichceta barbadensis, excepting that there are no setce upon the clitellum and that there are no genital papillce. In describing the last species, I pointed out that there is a gradual reduction in the three specimens of the setae upon the clitellum, which is accompanied by a reduction in the genital papillae. In the two specimens which I describe here as Perichceta hesperidum this reduction in number has culminated in the total disappearance of both the clitellar setae and the genital papillae. If it were not for certain differences in the internal anatomy, to which I shall call attention later, these facts would rather show that there is no necessity for separating the forms specifically. In the internal anatomy there are, however, differences. I should say, however, that I have only dissected one of the two individuals associated together here under the name of Perichceta hesperidum. In that worm the cceca are remarkably small as compared with those of other species. The intestine is provided with a fairly well-marked typhlosole ; it commences in the xvth segment. There are two pairs of spermathecce, which lie in segments vii. and viii. and open on the border-line between segments vii./viii. and viii./ix. ; in the case of the anterior pair, the displacement of mesentery makes the apertures, when viewed from the inside of the body, look as if they were placed in the middle of segment vii. The diverticulum is contorted. I only found a single pair of receptacula ovorum in place of the two pairs of the last species; they are attached to the front wall of segment xiii. and lie above the ovaries; they are elongate and lie obliquely on the septum. The atrium shows a difference of importance from the last species ; this is the presence of a terminal sac. This sac is, however, so extremely small in the present species that it needs careful looking PROC. ZOOL. Soc-1892, No. XII. 12 |