Benham. — E/7)'fItirnr?nii from Stephe?j Island aufl D'UrvilJf Islatul. 37 



5 mm., but, as usual, is somewhat less at about the 7th segment, which 

 is but 4 mm. across, and less again at the genital region, which is only 

 3 mm. It is evident that these measurements do not give a true idea of 

 the dimensions. 



The chaetae are equally spaced, so far as one can see on the animal. 



The clitellum, though not yet thickened, seems to cover segments 16-20, 

 for the intersegmental furrows are evanescent. Probably when the worm is 

 mature the clitellum extends farther forward than this. 



The spermathecal pores are conspicuous owing to their tumid lips. 



There is one external feature in which this worm seems to show a 

 marked peculiarity. On the ventral surface of the segments 17-19 there 

 is a rather deep rectangular trough, with well-defined lateral and terminal 

 boundaries, while the non-glandular floor is marked by longitudinal foldings. 

 The appearance is that this ventral region is withdrawn by internal 

 muscles (fig. 3). 



The longitudinal margins correspond to the level of the ventral couples 

 of chaetae, but on these segments, owing no doubt to the retraction of 

 the ventral region, which results in the formation of the trough, the ventral 

 chaetae and the nephridiopores are carried mediad of the line formed by 

 these structures in the neighbouring segments. Under a dissecting-lens 

 the chaetae themselves are not visible on these three segments, but the 

 ventral nephridiopores of segments 17 and 19 are quite conspicuous and 

 are out of the line. 



The porophores lie within this lateral margin, and are not prominent. 

 They project rather into the trough from the sides than from its floor, so 

 that the pores face inwards towards the middle line. 



The spermatic groove is very evident : its outer lip is formed on each 

 side by the edge of the lateral wall of the trough ; the inner lip is seen 

 lower down this wall. 



Internal Structure. — I did not note any specially thickened septa, as 

 everything is so soft. 



The dorsal vessel is single throughout the worm ; the last heart is in 

 the 13th segment. 



The gizzard belongs morphologically to the 6th, for the septum 5/6 

 is inserted at its hinder end ; but its " apparent " position is in the 8th 

 and 9th segments — that is, a transverse line across the body as dissected, 

 passing over its anterior end, cuts through the intersegmental furrow 7/8, 

 and its posterior end lies at the transverse line through 9/10. 



Oesophageal glands are large and spherical, and meet above the tubes 

 in 14th and 15th, while in the 16th is a smaller gland ; the intestine 

 commences in segment 20. 



The spermatheca has a large ampulla (larger actually than that of the 

 previous species) with a narrow duct, which carries a small racemose 

 diverticulum of the form usual in the genus (fig. 4). 



The penial sac, and consequently the copulatory chaetae, are not nearly 

 so long as usual. This, I think, is to be accounted for by the external 

 trough, which probably aids in the process of copulation in this species, 

 as it appears to do in certain other families of worms. But I can detect 

 no " arcuate " muscles in these segments. The penial sac is not only 

 relatively, but absolutely, smafler than in the previous species. Here it 

 is scarcely longer than the length of the segment, whereas in M. megacystis 

 it extends across the body-wall half-way towards the dorsal mid-hne. 



