286' Transactions of. the Society, 



Michael sen (Das Tierreicli, x. p. 49) translates Eisen's descrip- 

 tion, and places it as an uncertain species under Tnhifex. Beddard 

 regards it as a doubtful synonym for T. rivulorum. My notes show 

 either two distinct varieties of Ili/odrilus campanulatus Eisen in 

 England, or two species nearly related, and I am at present in 

 favour of regarding the one with S-shaped spermathecffi as true 

 /. campanulatv.s, and regarding the other as 1. homieti Clap. Should 

 this surmise prove correct we shall have got rid of much confusion, 



I have recently been engaged on the study of specimens collected 

 for me by Mr. C. Todd at the Tower Bridge. The spermathecae are 

 often filled with Nematodes which, when coiled, closely resemble 

 the spiral sperm atophores of Spirospcrma ferox Eisen. 



2. Ilyodrilus trichocluvtus Ditlevsen. 



I will first copy my original notes, then discuss the relation- 

 ship. A very small worm, 8-10 mm. in length, 60-65 segments, 

 fragile looking, but possessed of great vitality. Capilliform setse 

 2 in first five segments, tlien 1 gradually growing smaller, and 

 eventually dying out about segments 25-30 ; tail thin, yellow. 

 Forked sets 2-3 per bundle in anterior segments, teeth about equal ; 

 in posterior segments usually only 1 forked seta in each set. 

 Chloragogen cells begin in 6 and die out with capillary setas. 



First nephridium in 6/7, anteseptal very small, postseptal re- 

 markably developed. Enlarged vessels in segments 8 and 9, blood 

 system complex, front commissures, at least in 5 and 6, with valves. 

 Ventral vessel, as usual ; forks in the fourth segment. Brain, 

 small, incised behind, or with two lobes. Pharynx moving back- 

 wards as far as the setae of sediment 3. Front segments annulate : 

 1 broad and 1 narrow ring. Lumen of nephridia ciliated and 

 capable of rapid motion. 



In mud of the Thames at Kew, with Monopylephorus parvus, 

 Paranais, Helodrilus, and other Annelids, August 26, 1911. Not 

 found in adult stage. 



1904. — Ditlevsen (Zeitschr. wiss. Zool., Ixxvii. p. 427) describes 

 a worm as Monopylepliorus trichocluvtus ; but it cannot be a Monopyle- 

 phorus, since the organs are paired. Moreover, Monopylep)horus 

 has no capilliform setae. Everything points to Ilyodrilus or an 

 allied genus, but Ditlevsen's ideas of Ilyodrilus were confused, as 

 we see by his placing Rhyacodrilus in that genus. As my Thames 

 specimens agree in all essential points with Ditlevsen's, I retain his 

 specific name, although it loses its meaning when applied to an 

 Ilyodrilus, seeing that all the species in this genus are Trichochaetes. 

 The original may here be appended for comparison. 



" Monop]ilep)horvs trichochietus sp. n. In den dorsalen Borsten- 

 biindeln gibt es zwei fadenfeine, haarformige Borsten und zwei bis 

 drei gespaltene Hakenborsten, deren oberstes Astchen ein ganz 



