284 Transactions. — Zoology. 



transversely ovate, and the duct is scarcely distinguishable on 

 dissection, but receives right and left a small ovate diver- 

 ticulum with a long narrow duct. 



Plagiochseta rossii, n. sp. 



Locality. — Five specimens were collected in the bush on 

 the shore of Lake Te Anau in 1900. I name this species after 

 the collector, Mr. Donald Boss. 



The colour, in formol, is purplish-brown, with a darker- 

 brown median dorsal stripe. The preclitellar region is 

 greyish-brown. 



Dimensions. — The mature individuals vary from 105 mm. 

 to 165 mm. in the preserved condition. In a specimen measur- 

 ing 158 mm. its greatest diameter is 7 mm. at segment 8, 

 and also behind the clitellum. The preclitellar region is 

 20 mm. and the clitellum 11 mm. in length. This worm con- 

 sists of 112 segments. 



The prostommm is epilobic (three-quarters), without a pos- 

 terior groove. 



The chcetcz are about thirty-two to thirty-six in each seg- 

 ment, not in couples. Each chaeta is implanted in a light 

 spot. There is no perceptible diminution anteriorly, for I 

 count thirty-two on the 7th segment and thirty-four on the 

 3rd segment. There are small ventral and dorsal gaps, but no 

 lateral gap, the series of sixteen or eighteen chaetae on each 

 side being practically equidistant. 



The clitellum extends from 13th to 17th segment, and in 

 the largest individual the 18th segment differs in colour from 

 the 19th, and looks as if it, too, would become part of the 

 clitellum. The organ is continuous ventrally in its anterior 

 region, but on segments 16 to 20 is a white transversely oval 

 genital area, containing the genital pores. 



Genital Pores. — The porophores are prominent. There is 

 no true spermatic groove, but a ridge passes from 17th to 19th 

 segment on each side, having a rather peculiar arrangement. 

 Starting from the 17th porophore, the ridge curves down the 

 posterior face with an outward sweep and reaches the inter- 

 segmental furrow, where it disappears. A similar ridge occurs 

 on the anterior face of the porophore on the 19th segment. 

 Then in the 18th is a curved ridge, convex outwards, con- 

 necting the two other ridges. The ridge is a rounded pro- 

 minent structure, forming the outer boundary of an indistinct 

 furrow whose inner boundary is formed by the glandular 

 tissue of the body. This ridge seems to contrast with the 

 definite groove found in many Acanthodrilids, for in them the 

 groove is the conspicuous structure ; here, in Plagiochceta, it 

 is the external (and only) ridge that catches the eye. How 

 far we may distinguish these two things is uncertain, but the 



