^ovTH^RN— Monograph of the British and Irish OligochcEta. 155 



Mesenchytrseus setosus, Mchlsn. 



1900. M. s., Michaelsen in Tierreich, x., p. 85. 



1901. 31. niegachadus, Bretscher in Rev, Suisse Zool., ix., p. 210. 

 1907. M. s., Southern in Irish Nat., xvi., p. 71, PI. 19, fig. 6. 

 October, November, December. 



Habitat — Ireland. Carrantuohal, Co. Kerry ; Lambay. 

 Distribution — Germany ; Switzerland. 



Mesenchytrseus Beumeri (Mchlsn.). 



1900. M. h., Michaelsen in Tierreich, x., p. 86. 



June. 



Habitat — Ireland. Carrantuohal, Co. Kerry. 



Distribution — Germany. 



Mesenchytrseus celticus n. sp. 

 Plate XL, fig. 13, A-G. 



These worms are very large and thick in proportion, and of very soft 

 consistency. The anterior end is white, or faintly yellow, whilst the middle 

 and posterior parts are much darker. Microscopical examination shows that 

 this is due to the large number of small dark coelomic corpuscles, very few 

 of which pass in front of the 6th segment. The length of the living worm 

 varies very much according to the state of contraction. The same individual 

 may vary from 12-25 mm. Preserved specimens are 10-15 mm. long and 

 1 mm. broad. The set^e are very numerous and all of the same size. The 

 anterior ventral bundles usually contain 10 or 11, occasionally 12 or 13 setae. 

 The lateral bundles contain 5-7 setae. The head pore is situated at the tip 

 of the prostomium (PI. xi., fig. 1 3, a, a). The latter is tliickly covered with 

 prominent papilke. The epidermis is very granular, and is covered with rows 

 of irregular amoeba-shaped isolated glands (fig. 13, b). The clitellum is 

 very prominent. In the Irish specimens it occupied segments |1I-13, in 

 the Scotch specimens segments 12-14. The dorsal vessel appears to be 

 intraclitellar in origin, rising about the 13th segment. The coelomic 

 corpuscles are very numerous (fig. 13, c). They are small, oval, and full of 

 very dark granules. There are seven pairs of septal glands in segments 4-10. 

 The brain (fig. 13, D) is concave in front and behind, and its breadth 

 considerably exceeds the length. The nephridia (fig. 13, e) are of the 

 characteristic generic structure, consisting of a short, slender anteseptal, and 

 a large bilol^ed postseptal. The duct is long and slender, and appears to rise 

 between the two lobes, or from the base of the larger one. The spermatheca^ 



