282 Transactions. — Zoology. 



Plagiochaeta lateralis, n. sp. 



Locality. — The shore of Lake Thompson, 1,100 ft. above 

 sea-level, on the track from Lake Te Anau to George Sound. 

 Collected by Mr. J. Mackenzie. 



Colour. — Pale-greyish, with dark-brown clitellum. 



Dimensions. — The longest of the dozen specimens mea- 

 sures 55 mm., with a diameter of 5 mm. The body is rather 

 depressed, with a slight groove along the median dorsal and 

 ventral surfaces. The number of segments is 100. 



The prostomium is half epilobic, with a transverse furrow 

 before the end of the longitudinal furrows. 



The chata are twenty-four (about) in each segment. 

 They are not in couples, but are arranged in two groups on 

 each side, an upper and a lower, separated by a distinct 

 lateral gap, which peculiarity suggested the specific name. 

 The lower group consists of five chaetae, the upper group of 

 seven chaetae ; the latter are further apart than the former. 

 The dorsal gap is greater than the ventral, and each is greater 

 than the lateral. The arrangement may be represented by 

 the following formula, in which the vertical lines represent 

 chaetae and the numerals indicate the relative distances, as 

 measured by an eye-piece micrometer on the flattened skin. 

 V, L, and D are the ventral, lateral, and dorsal gaps re- 

 spectively. 



9 | 2i | 2 | 2i | 2i | 5* j 3 | 3 | 4 | 4 | 3 | 4 | 12. 

 V a bed e L f g h i j k I D 



No doubt the actual distances vary, not only in different 

 specimens, but in different parts of the body. 



The clitellum covers segments 14 to 17 inclusive ; it does 

 not extend over the ventral surface, but ceases at about the 

 level of the porophores. 



Genital Pores, dc. — The porophores are feebly developed 

 on 17 and 19, and are in line with about chaeta e — i.e., almost 

 laterally placed. There are four chaetae below each, and four 

 chaetae below the male pore in 18th segment ; and sections 

 show a 5th chaeta close to the pore in each of these segments. 

 These chaetae are further apart on these segments than else- 

 where. There is a distinct and curved spermatic groove^ 

 convex outwards. In some of the specimens copulatory 

 tubercles exist, but asymmetrically on the right or left of 

 segments 18 or 20. In none are they fully developed, when,, 

 no doubt, they will be paired. 



The oviducal pores are in line with the gap b/c, the 

 spermathecal pores between 7/8, 8/9, in line with the chaetal 

 gap e/f ; and in several of the individuals there is a pair of 

 pitted tubercles on the 8th segment, just behind the chaetal 

 ring, in line with the gap dje. 



