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Show 1886.] LITTLE-KNOWN E A R T H W O R M S . 299 Dendrobana,&c.), there have been described more species of Perichceta than of any other genus. Rather more than thirty have been named, but several of these, as Dr. Horst1 has pointed out, are merely synonyms, while a large number have evidently been too imperfectly characterized to admit of recognition. In the majority of cases the number of tbe spermathecae and the absence or presence of variously formed diverticula have proved useful as specific characters; but species have been distinguished on other grounds which happen to agree in the number and form of the spermathecce. The presence of genital papillae is almost universal in the genus Perichceta, and these are placed either in the neighbourhood of the spermathecae or of the reproductive apertures ; this character serves to differentiate P. indica from P. affinis, which otherwise agree pretty closely in structure. I have bad the opportunity of examining a number of specimens of both these species as well as of an apparently new species which is closely allied to both. A few notes therefore, which will perhaps serve more clearly to define these species, may be worth adding to what is known about them. Of Perichceta indica I have received about half a dozen specimens from New Caledonia though thekindnessof Mr. E. L. Layard, C.M.G. The specimens were of varying size, the largest individuals reaching a length of some 6 inches. Their colour (in alcohol) was a very dark brown, with an indistinct whitish line in the middle of each segment, marking the insertion of the setae. The latter are remarkable for the fact that one or more on either side of the ventral median line are very much larger than the rest: this fact has already been noted by Horst (Nederl. Arch. &c. loc. cit.), and a similar variation in the size of the setae occurs in Perrier's species P. luzonica and P. biserialis2. The two last-mentioned Perichata have up to the present been but briefly described ; but the description is sufficient to show that they cannot be confounded with P. indica. P. bisei-ialis has only two pairs of spermathecae and several pairs of genital papillae in the segments following the 18th, while there are four pairs of spermathecae in P. indica. In P. luzonica the clitellum occupies four segments. Dr. Horst mentions two pairs of genital papillae placed respectively upon segments 7 and 8 ; in one of m y specimens there were three pairs, the third pair being upon segment 6. Another important variation is in the number of segments which compose the clitellum : in most of the individuals where the clitellum was developed, it was found to occupy segments 14-16 inclusive, as described by Horst for this species and as commonly found in the genus. In one specimen, however, the clitellum was a segment short, being developed only upon the 14th and 15th rings ; the clitellum was fully developed upon these segments and sharply defined, as it usually is in this genus. It is of some importance to note this fact, since a species of Perichceta, P. bicincta, has been characterized mainly on account of the restriction of the clitellum to two segments. 1 Notes from the Leyden Museum, vol. v. p. 186. 2 Comptes Eendus, t. lxxxi. (1875) p. 2044. 20* |