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Show 1890.] WOHMS OF THE GENUS PERICH_ETA. 55 If Rosa's definition of the two genera be slightly altered, it will be possible to arrange most of the species of "Perichceta" as follows:- MEGASCOLEX. Line of setae interrupted; clitellum occupying more than three segments. PERICH_ETA. Line of setae continuous; clitellum consisting of three segments only. There are, however, other species which present more important differences among themselves than those above mentioned. Prof. Bourne (11) calls attention to the fact that there are anatomical differences, to which considerable weight must be attached, between several of the forms described by him. Perichceta novce zelandice (Beddard, 7) differs from all other species in the following combination of characters : - N o dorsal pores ; nephridia paired ; atria tubular. P. bakeri and P. barronensis of Fletcher agree in their nephridia and atria, but have dorsal pores. A number of species described by Fletcher (17), viz. P. attenuata, P. enormis, and P. coxii, agree to differ from others in the very remarkable fact that the setae in the anterior segments are eight in number to each segment, increasing in the posterior segments to 20-30. In both these cases the different geographical area occupied by the species is, perhaps, a further argument in favour of separating them. Then Perichceta stuarti has four pairs of atria, as in Acanthodrilus they open on to the same segments as in that genus, and appear to be similar in structure; the diverticula of the spermatheca also appear, from Bourne's description (11. p. 667), to be more like those of Acanthodrilus than of most Perichceta. P. ceylonica (Beddard, 9) has two distinct pairs of atria, but they open both of them on to tbe same segment, the 18th; at present I am not inclined either definitely to unite this form, generically, with P. stuarti, or definitely to separate it; further information as to its structure is first needed. If these various types be accepted by zoologists as of generic value, it must still be admitted that they cut off very small comers from the mass of species (about sixty in number) of which the family consists. At present, however, it does not seem easy to make any further alterations, and I am not satisfied that Megascolex has the same value, as a generic type, that Aporochceta has. The following is a definition of the family Perichaetidae and its various genera as advocated in this paper. Fam. PERICH^ETID-E, Claus. Earthworms with a continuous circle of numerous setae round all the segments of the body (with the occasional exception of a few of the most anterior); clitellum commencing with the thirteenth or |