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Show 1886.] MR. F. E. BEDDARD ON A LARGE EARTHWORM. 16!) drilu.il. This genus is already known to inhabit New Caledonia ; M . Perrier has described two distinct species from that region. The species which forms the subject of the present communication may be identical with one or other of these. The descriptions given by M . Perrier of Acanthodrilus obtusus and A. angulatus are necessarily insufficient, owing to the poor condition and immaturity of the specimens at his disposal ; but certain facts, such as the position of the generative apertures and of the clitellum, could hardly be mistaken even in specimens greatly injured through bad preservation ; in these points the present species differs from both of those described by Perrier, as will be apparent from the following notes on its structure. External Characters.-I have sketched (Plate XIX. fig. I) the anterior segments of the body from the dorsal aspect to indicate the main external features which are visible upon that surface. The buccal lobe divides the first segment2, as also in A. dissimilis and A. novai zelandice, two species recently described by myself3. Of a fourth species of the genus, viz. A. verticillatus, M . Perrier writes 4 : - " La lobe cephalique n'entame pas le premier anneau et parait an contraire s'elargir asabase demanierearessembleralapartiesuperieure d'un trefle ; mais cette apparence tient peut-etre a un etat particulier de conservation." I mention these facts because the genus Lumbricus has been split up into other genera mainly on this account. It does not appear to me advisable, while there are so many internal structural differences, to make use of so small an external character for classificatorv purposes ; but in the case of the genus Acanthodrilus this mark of difference between species appears to be correlated with other differences of structure, inasmuch as M . Perrier hesitates to include A. verticillatus in the same genus with A. obtusus; the male generative pores in the former species are upon the 17th and 18th segments and are not separated by an intercalated segment as in the latter and all the other species of the genus at present known. On either side of the buccal lobe, and consequently between the first and second segments of the body, is a single pore; these may perhaps correspond to the single median dorsal pore which is the only orifice of the kind found in the Oligochseta limicolse. The' clitellum was fully developed in several specimens, and extended from the 13th to the 17th segments inclusive, with the exception of a portion of the 13th segment; the glandular tissue composing the clitellum was only visible on the posterior half of that segment; the clitellum extends occasionally for a short distance on to the 18th segment. The anterior region of the clitellum down to the 15th segment completely encircles the body ; the 1/th and 18th segments, on the contrary, have a very considerable median area upon which there is no glandular development; the lateral margins of this 1 Perrier "Eecherches pour servir a fhistoire des Lombriciens terrestres," Nouv. Arch', d. Museum, t. viii. (1872) p. 85. 2 I have reckoned the first seta-bearing segment as the second segment of the body in common with the majority of naturalists who have studied this group. 3 P. Z. S. 1885, p. 813. 4 Loc. cit. p. 93. PROC. ZOOL. Soc-1886, No. XII. 12 |
