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Show 54 MR. F. E. BEDDARD ON [Feb. 4, in one or both of the following characters:-(1) in the ring of setas upon each segment being discontinuous at one or more points ; (2) in the clitellum occupying more or fewer segments of the body than three." Rosa has lately pointed out (24) that m y distinctions are valid, but that the names should be reversed. I am now quite prepared to agree with him ; at the time when I wrote I was inclined to consider that Templeton's Megascolex was identical with Perichceta, even to the extent of having a continuous circle of setae in each segment, inasmuch as Baird (1), who had examined the type in the British Museum, stated that he could find no difference between it and Perichceta. Taking for granted the accuracy of Baird's observations, it appeared to me necessary to use the name Megascolex for the worms which Schmarda termed Perichceta; strictly speaking I should have allowed the name Perichceta to drop, but it was proposed to retain it for perichcetous worms with a dorsal and ventral interrupted line &c. When I discovered (4) that my Pleurochceta was identical with Templeton's Megascolex cceruleus, it seemed necessary to restrict the generic name to that form, and to group all the other known perichcetous forms under the genus Perichceta; it will be seen that the definition of Perichceta appended to that paper includes such forms as P. armata, though I omitted to state in so many words that it was proposed to drop the generic distinction between Megascolex affinis and Perichceta armata, since the differences between Megascolex cceruleus and any other perichaetous worm are rather more important than those which differentiate the latter species among themselves. Rosa (24) has, as already stated, proposed to divide Megascolex from Perichceta by the distribution of the setae and the presence or absence of intestinal caeca; the genera are thus defined by him :- Megascolex. Line of setas interrupted ; no intestinal caeca. Perichceta. Line of setae continuous ; intestinal caeca present. Fletcher (17, in.) has proposed a similar division, but also (17, n.) has pointed out that in the typical Perichceta, with continuous row of seta? and caeca, the gizzard is situated further back than in Megascolex and occupies two segments, the mesentery between them having vanished1. This distinction, although it applies to so large a number of species, falls to the ground before the Indian species described bv Prof. Bourne2; Perichceta hulikalensis (Bourne, 11. p. 0*G8) has dorsal and ventral gaps, but possesses intestinal caeca in the usual position. 1 I had previously directed (6) attention to this difference between certain species of Perichceta, though mistaken in supposing that in P. newcombei the gizzard occupied three segments ; I have since convinced myself the giziard is really in segment 6; in any case this species does not fit in very accurately with the proposed subdivision of Perichceta. - This paper was overlooked by Eosa, as he mentions in a postscript (24 p. 11). |