542 OLIGOCHAETA 



distinguish the species. The apparent differences in the genital papillae are of less 

 weight, as there is much variation in these structures. 



(17) Acanthodrilus aquarum-dulcium, BEDDAKD. 



A. aquarum-dulcium, BEDDARD, P. Z. S., 1893, p. 680. 



A. georgianus, BEDDARD, Q. J. M. S., vol. xxx, 1890, p. 421 (in part.). 



Definition. Length, 47 mm. ; diameter, 3 mm.; number of segments, 90. No specially 

 thickened septa. Penial setae with a series of minute denticles at free end. In other 

 respects like A. falclandicus. Hal. Falkland Islands; in fresh water. 

 I originally confounded this species with A. falclandicus, or, as I then called it, 

 (erroneously) ' georgianus.' Later its differences from that species were pointed out; 

 there can be, I think, no doubt of its distinctness. The chief difference is in the 

 form of the penial setae. The worm also is of a much more slender build than 

 A. falclandicus, which has possibly something to do with its aquatic habit. I have 

 not used the papillae as differential characters as these structures are so apt to vary 

 that they must be used with the greatest caution, and, indeed, I have endeavoured 

 never to rely entirely upon them. In specimens of this species examined as 

 transparent objects in glycerine, there were to be seen two pairs of papillae lying 

 between the ventral setae on each of segments xviii, xx a pair to each that is to 

 say. This species may also differ but this is perhaps very doubtful from the last 

 in the fact that it has egg-sacs which I did not observe in A. falclandicus. 



(18) Acanthodrilus bovei (ROSA). 



Mandane Bovei, ROSA, Ann. Mus. Civ. Geneva, vol. vii (2a), 1887, p. 143. 



Definition. Length, 35 mm.; diameter, 3 mm. ; number of segments, 100. Prostomium 

 prolonged over two-thirds of buccal segment. Clitellum, XIII XVI, rendered incomplete 

 on last two segments by a triangular area of non-glandular epidermis. Setae in eight 

 series, distance between which increases dorsally. Male pores correspond in position 

 to second setae. Spermalhecal pores are related to the same setae. Papillae, two pairs 

 on X, XI, between ventral setae; a median papilla on IX. Penial setae ornamented 

 with 'large obtuse tubercles' Spermathccae in VIII, IX, each with two diverticula 1 . 

 Halt. Puntarenas, Straits of Magellan. 



1 ' Nefridiopori e port dorsali non visti ' (Rosx). 



