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Show 1892.] SPECIES OF EARTHWORMS. 679 The differences between the two forms may be stated in a tabular form as follows :- Setce.-In A. georgianus the distance separating the two setae of the lateral couple is hardly greater than that which separates the ventral couple. In m y species, which I propose to call A. falclandicus, the distance between the lateral setae is markedly greater than that between the ventral setae. Nephridiopores.-In A. georgianus these are placed in front of and below the third seta. In A. falclandicus these pores are directly in front of the third seta of each segment. Gizzard.-Totally absent in A. georgianus. Rudimentary in A. falclandicus. Penial setce.-In A. georgianus these have fewer tubercles upon the extremity and these tubercles have no serrations. Michaelsen goes on to suggest that my species is possibly identical with Rosa's Acanthodrilus bovei. I am not able, however, to adopt this suggestion, and for the following reasons. In the first place Acanthodrilus bovei is a much smaller species than the one named by myself Acanthodrilus falclandicus; the measurements of A. bovei are 35 m m . in length by 3 m m . in diameter ; A. falclandicus measures 60 m m . in length and upwards. Of A. bovei the prostomium is said by Rosa to extend on to the buccal segment for about two-thirds of the length of the latter ; the prostomium is less extensive in A. falclandicus. The clitellum in A. falclandicus is quite complete, extending right round the body ; in the species with which it is sought to identify m y A. falclandicus there is a non-glandular triangular area reaching as far forwards as the xvth segment. Acanthodrilus falclandicus possesses a pair of papillae upon the xth segment which lie behind the ventral setae-exactly behind them. In A. georgianus Michaelsen has described a similar pair of papillae upon the tenth segment, but not anything is stated with regard to their position upon the segment except that they lie upon the seta-line 2. In A. bovei there are such papillae, but they lie between the ventral setae on segments x. and xi.; Rosa also speaks of an oval area occupying a median position upon the ninth segment. These differences are, I think, sufficient to distinguish m y species from Rosa's Acanthodrilus bovei1, though doubtless the two are very nearly related. In m y paper upon the anatomy of this form I referred to its occurrence in fresh water as well as upon the land ; I have since re-examined more carefully the specimens which occurred in water, and I find that they are really different from A. falclandicus, though very nearly related ; indeed the differences between all of these Patagonian Acanthodrilidae are not very large. 1 " I Lombrichi della spedizione antarctica italiana del 1882," Ann. Civ. Genova, ser. 2 a, vol. vii. p. 143. |
