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Show 358 MR. F. E. BEDDARD ON [May 3, present species, however, there is no doubt of their lying in the xth segment. The sperm-sacs are in segments x. and xi. They partially involve the testes and vas deferens funnels. The ovaries are, it is almost unnecessary to state, placed in segment xiii. The oviducal funnels open opposite to them ; the ovaries are so large that but little room is left between the end of the ovary and the funnel; I saw an ovum within the mouth of the oviduct. There are no egg-sacs. The oviducal pores are upon the xivth segment. In the viiith and ixth segments are the spermatothecse. These organs are large sacs, communicating with the exterior by means of a comparatively long duct; they were densely packed with spermatozoa, but had no diverticula. It is evident from the above short and, in some respects, incomplete account of the Pilcomayo worm that it is most nearly allied to the genus Acanthodrilus. That genus, it should be remarked, is one which is less uniformly terricolous than any other genus of " earthworms." There are already several species known to occur in water. Among them are Acanthodrilus stagnalis, A. dalei, A. schmardce. This is, however, the first species which has been met with in saline waters. The other aquatic Acanthodrilidae show no particular affinities to aquatic genera ; but the present species does; and it distinctly approaches Ocnerodrilus. The resemblance is not only in the simplification of the structure of the atria ; that of itself would not perhaps be a very important fact, since it might be put down merely to degeneration. A more important point of likeness is the existence of the single pair of oesophageal diverticula in segment ix.; this particular segment is not a usual one in which to find these calciferous glands. Besides, in other Acanthodrilids there are nearly always two or three pairs of these glands situated further back. Very little is wanting to convert the species here described into an Ocnerodrilus; to refer it definitely to the genus Acanthodrilus would be to ignore the characteristic differences which it shows from that genus, with which, however, it undoubtedly agrees in all those points which are made use of to define the genus Acanthodrilus. O n the other hand, it can hardly be put in the genus Ocnerodrilus. The principal difficulty in the way of this is the two pairs of atria and their position. The fact of there being two pairs of atria instead of one only would not deter m e from this step ; I think, for instance, that the genus Neodrilus must be merged in Acanthodrilus. The important difference appears to be the separation of the atrial and vas deferens pores by a septum in Acanthodrilus. If it were not for the position of the calciferous glands all the resemblances between this worm and Ocnerodrilus might fairly be set down to a convergence due simply to degeneration. As it is I a m inclined to think that it will be necessary to institute a separate genus for this Acanthodriloid worm from the Pilcomayo ; and I propose to call it Kerria, after Mr. Graham Kerr, with the specific term halophila. It may be useful to compare, by means of the following table, the |