of OUgochcetous Annelids. 93 



part in Limnodrilus. This is a very important distinction. A 

 further character is found in the spermatophores (bodies oc- 

 curring in the spermatic reservoirs, which I have shown to be 

 agglutinated masses of spermatozoa, and on which Clapar^de 

 founded his genus of parasitic Opalinoid parasites, Pachyder- 

 mon). In the new form these are elegant and tapering at 

 each end, whilst in T. rivulorum they have a curious conical 

 extremity, due to moulding in the mouth of the reservoir. 

 On describing the setse of this new form to Prof. Leuckart, 

 last April at Leipzig, he told me that he had just seen a de- 

 scription of such setae, and handed me a Russian work, ' The 

 Memoirs of the first Meeting of Russian Naturalists at St. 

 Petersburg, 1868, Supplement,' in which is a paper entitled 

 " Materials for the knowledge of Onega Lake and Territory in 

 their Zoological Aspect," by Karl Kessler. By the kindness 

 of Dr. Alexander Brandt, who was fortunately present, I was 

 made acquainted with the contents of this paper. Several 

 Oligochastous Annelids are imperfectly described, and among 

 them Scenuris or Naidina umhelUfera, which is evidently the 

 new Thames worm, though no anatomical details are given, ex- 

 cept that the genital openings are in the ninth and tenth fascicu- 

 late segments. The palmate setge are figured, but not well, and 

 it is obvious the artist had not a very high-power microscope. 

 Six specimens were obtained from mud by Lake Ladoga ; and 

 the specific name " umheUifera " is given, which I therefore 

 accept for the Thames worm, which stands as Tuhifex umhel- 

 lifer. The genital openings in this species are placed as in 

 the T. rivulorum^ with which it is associated, viz. those of the 

 spermatic reservoirs in the ninth fasciculate segment, those of 

 the male ducts in the tenth fasciculate segment. The number 

 of setae and their form in a well-developed specimen were as 

 follows : — (1) Ventral, 3 of « (fig. 1) ; Dorsal, 5 of 5 (fig. 1) 

 and 2 capillary seta3. (2) V. 4 of a ; D. 5 of h, 3 cap. (3) V. 

 4 of a (larger) ; D. 8 of i (larger) , 3 cap. (4) V. 3 of a ; D, 

 9 of 5, 4 cap. (5) V. 3 of a ; D. 8 of Z>, 3 cap. (6) V. 3 of 

 a ; D. 8 of Z*, 4 cap. (7) V. 2 of a ; D. 5 of Z», 3 cap. (8) V. 

 2 of a ; D. 5 of ^, 2 cap. (9) V. 3 of a (small) ; D. 4 of h, 

 1 cap. (10) V. 2 of a (small) ; D. 2 of Z*, 1 cap. (11) V. 2 

 of c ; D. 3 of c, 1 cap. (12) V. 2 of c ; D. 2 of c. (13-18) 

 same as (12), then 2 of c in each ventral and 1 of c in each 

 dorsal fascicle, with no capillary set^e for the rest of the worm. 

 This specimen was not in a sexual state, though of large 

 size (1| inch). 



It is a question whether Tuhifex umhellifer has been intro- 

 duced into the Thames by ships. It is very abundant in parts. 



3. Set<B o/Tubifex rivulorum. — A careful study of the setae of 



