KONGL. SV. VET. AKADEMIENS HANDLINGAR. P.AND 15. N:0 7. 15 



The testes are all situated in front of the cingulum (segments 11 and 12). 



The ovaries are, contrary to those of other species, situated partly behind the 

 cingulum (fig. 46). 



The perigastric cells are opaque, oval, or circular, and smaller than those of the 

 preceding species (fig. 2. g). 



The three species belonging to the subgenus Mesenchytrceus are all of a light 

 milky colour, with the segments well defined, every segment sometimes being again seg- 

 mented. Most individuals have a tendency to bend themselves like a sickle and espe- 

 cially so M. falciformis. Its minuteness makes it also easily distinguishable from its 

 allied forms, but hardly from small individuals of Archienchytrceus Lévinsenii which 

 species it resembles both in colour, form and size. 



From the two preceding species it is well distinguished not only by the shape 

 of its receptacle, the screwlike enlargement of the efferent duct, the form of the head- 

 ganglion, but perhaps easiest through the number and location of the ovaries which oc- 

 cupy not only the segments of the cingulum, but also the four segments behind, viz. 

 the 13 th , 14 th , 15 th and 16 th segments. 



This character will also distinguish this species from all other forms of the ge- 

 nus Enchytrceus sens. lat. which I have had occasion to dissect. The ovaries are not 

 floating but affixed to the body wall. Enchytrceus vermicularis is said to have floating 

 ovaries behind the cingulum as a rule. 



In all the species of Mesenchytraius the spines are curved and of the same length 

 and generally in bundles of two, the largest number of course always belonging to the 

 ventral fascicles. 



Length. of body 4 — 5 ra. m. 



Width » » Vs m. ra. 



Spines 5. 6. 6. 5. curved and of the same length. 



Number of segments about 50. 



Habitat. The northern shore of Matotschkin Scharr is the only locality where 

 this species was collected. 



Archienchytraeus n. 



A. The receptacle consists of a simple tube neither enlarged nor furnished with 

 any follicle for the spermatozoa. 



A'. No perigastric cells .... A. Lévinsenii. 



A". Perigastric cells are numerous ... A. tenellus. 



B. The receptacle consists of a larger tube, generally on the raiddle or near the 

 top enlarged or differentiated to a receptacle proper. 



B'. The enlargement is sacklike, situated at the top and very large . . . 



A. lampas. 

 B". The enlai'gement is below the top of the organ and very short . . . 



A. Dicksonii. 

 B". The enlargement begins at the middle but is not säck- nor bladderlike. 



