228 PROF. AY. B. BEXHAM OX AQUATIC [NoV. 3, 



occuiTence in this country of a genus so abundant in Australia, 

 of which the Earthworm fauna is so entirely distinct, for our 

 aquatic worms have, as yet, been scarcely touched. 



Plutellus lacustris, sp. n. (Plate XXYI. figs. 32-40.) 



Six hauls in Lake Wakatipu brought up specimens of a worm 

 which in some respects resembles Pontodrilus. 



The collection consists of 24 individuals, some few fully mature ; 

 others of full size, but without a clitellum ; and still more quite 

 young. One haul (No. 5) contains a number of cocoons, which 

 from their size probably belong to this species. 



The worms, as preserved, are robust in form, greyish in colour, 

 but the body- wall behind the clitellum is translucent. Those that 

 are well preserved have much annulated segments : three and 

 four annuli anteriorly, but more in the posterior segments. 

 The anterior segments are very short. 



The prostomium is relatively long, equal in length to the fii"st 

 two segments ; it is narrow, only half the breadth of the peri- 

 stomum, into which it is not embedded. It is prolohic. 



The chcetce, eight per segment, are isolated ; their formula is 

 approximately thus : aa = 2 ab; ab = ^bc; be = cd; dd = about 

 2 aa. The spacing differs somewhat in the anterior and posterior 

 regions ; aa is greater and be is rather less anteriorly than in the 

 greater part of the body (fig. 32). 



The cha3t£e are of the usual form (PI. XXYI. figs. 33, 34), 

 but are ornamented with a number of extremely fine crescent- 

 shaped marks near the distal extremity ; such as occur in the 

 genus Rhinodrilus and others, including Pontodrilus berniud- 

 ensis Bedd. and P. insularis Rosa. 



The chagt?e, both dorsal and ventral, of segments ii., iii., iv. are 

 smaller than those of the body generally, attaining only half the 

 length of the latter ; but the increase is gradual, as the following 

 measurements show : — 



Ventral chseta of segment ii. measures '015 mm. 

 „ .V. „ -0225 „ 

 >> ,, IX. „ 'Uo ,, 



„ „ xvii. „ -05 „ 



The ventral chsetse {a and b) are absent on segment xviii., being 

 here replaced by a couple of copulatory bristles on each side in 

 line with chseta b. 



The clitellum, in the most fully- developed individuals, i. e. in 

 three out of five clitelliferous worms, extends from | xiii. to end 

 of xvi. {i. e. 3| segments), the hinder boundary being,' in each case, 

 very well marked ; it completely encircles the body. 



The male genital pores on segment xviii. are in the line of 

 chseta b ; they are quite minute, and are not indicated by any 

 papillae ; but the ventral region of this segment differs in appear- 

 ance from the rest, and is seen to be glandular in transverse 

 sections. In one case this area was somewhat depressed, by the 



