DESCRIPTIONS OF GENERA AND SPECIES 529 



moreover (? always), there are three pairs of them in segments xiv, xv, and xvi. In 

 Acanthodrilus, on the other hand, the calciferous glands present the appearance 

 of swellings of the oesophagus ; they are commonly fewer than three pairs, and they 

 are often (as in A. georgianus and A. ungulatus) completely absent. In all the 

 species of Acanthodrilus which I have myself examined with reference to this point, 

 viz. A. novae-zelandiae, A. dissimilis, A. smithii, A. ungulatus, A. capensis, A. pictus, 

 A, georgianus, A. falclandicus, and A. aquarum-dulcium, the ventral setae of segment 

 xviii are present. In Benhamia crassa, B. stuhlmanni, and B. whytei these setae are 

 absent; whether this is a character of generic value remains to be seen. 



That the Acanthodrilidae with a diffuse nephridial system are near to those with 

 paired nephridia is shown by the difficulty of getting characters other than this for 

 distinguishing the genera. Furthermore there are special characters, confined to a very 

 few species of Acanthodrilidae, which occur indifferently in members of more than 

 one genus. The most striking example of a structure such as I refer to is the 

 existence of the copulatory setae (as HORST terms them) and glands in the neigh- 

 bourhood of the spermathecae in Benhamia beddardi, and in A. ungulatus and 

 A. schmardae. So also the double dorsal vessel completely double characterizes 

 the earlier genus Octochaetus (three species) and Diplocardia communis. The ' pepto- 

 nephridium,' so characteristic of Octochaetus, is also met with in A. annecte.ns, A, 

 paludosus, A. littoralis, and the genus Trigaster. 



The South American species form a more or less marked group ; as compared 

 with the New Zealand species indeed a well-marked group. They are all of small 

 or moderate size. The clitellum is not extensive xiii-xvi or xvii. Dorsal pores 

 are usually wanting. The only species of Acanthodrilus with no more than a single 

 paii- of testes and vasa deferentia occur in this group. The dorsal vessel is invariably 

 single. Calciferous glands are absent as specialized structures in all the species in 

 which they have been carefully looked for, the vascular and much plicated walls of 

 part of the oesophagus doing duty for them. If it were not for the Australian species 

 I should be disposed to emphasize the above characters by separating off the 

 Patagonian, Argentine, and Chilian Acanthodrilidae as a genus. The Australian species, 

 however, are all of them so imperfectly known that it would be, in my opinion, 

 unwise to attempt any such division of the genus Acanthodrilus. For A. macleayi 

 has a clitellum comprising, as in the South American species, a small number of 

 segments, while A. australis agrees with the New Zealand species in having a more 

 extensive clitellum (xiii-xix). 



The New Zealand species of Acanthodrilus nearly all agree to differ from the 

 species found elsewhere in that the nephridia are alternate in position. The only 



3* 



