24 GUSTAF EISEN, ON THE ARCTIC OLIGOCH^ETA. 



Neoenchytraeus n. 



I. The anterior margin of the cerebral ganglion is concave. 



A. The receptacle consists of a long and simple tube neither swelled nor fur- 

 nished with any receptacle proper ... N. fenestratus. 



B. The receptacle consists of a very short tube furnished at the top with a large 

 receptacle proper. 



B'. The inner tube of the segmental organs is very short and the outer one is 

 thick and pressed close to the middle lobe. 



a. the receptacle is twisted ... JV. Vejdovshyi. 



b. the receptacle is not twisted ... N. Stuxbergii. 

 B". The inner tube of the segmental organs is of the same length as the middle 



lobe, and the outer one is neither very thick nor pressed close to the middle lobe.... 



N. hyalinus. 



II. The anterior margin of the cerebral ganglion is convex. 



C. The receptacle consists of a long tube, furnished at the top with a bottle like 

 receptacle . . . N. callosus. 



D. The tube of the receptacle furnished with bladders. 



a. the cerebral ganglion is triangulär: N. durus. 



b. the cerebral ganglion is oblong: N. Raizelii. 



1. Neoenchytraeus fenestratus n. sp. 



Pl. IX. Fig. 17. 



The supra-oesophagial ganglion is very broad behind or nearly as broad as long. 

 In front it is considerably narrower (fig. 17, f). 



The receptacle consists of a long and narrow tube about 20 times longer than 

 broad, and very much resembling that of Archienehytrcms Levinsenii, only somewhat 

 longer (fig. 17. g). 



The segmental organs have the outer tube narrow, and longer than the middle 

 lobe, and the inner tube seems to be shorter. These organs resemble those of A. tenellus 

 and Levinsenii. 



The perigastic cells are large and circular or even somewhat irregular, with a 

 large plain nucleus, and in general resembling those of A. tenellus (fig. 17. h). 



The ovaries are very large in the 1 l. th and 12 th segments. 



The testes in the 9 th and 10 th segments. 



The spines are of equal length or the inner ones are larger, the fascicles being 

 fanshaped, and the spines in each being about 5. 6. 7. 5 (fig. 17. d). 



The length of the body about 15 to 20 m. ra. 



The width. of the same about 1 m. m. 



The number of segments about 60 very well clefined. 



