BRITISH ANNELIDS. 33 



tion. It lives among the roots of grass on the margins of stagnant 

 or running water, and is often with difficulty distinguished from the 

 mud-covered rootlets. To what extent its colour is strictly protective, 

 or due to its food and other factors, is not yet ascertained ; but it is 

 known to vary greatly. I have found a rich golden variety in Cum- 

 berland and Yorkshire, while elsewhere I have obtained specimens 

 ranging from a dull brown to a bluish, iridescent colour through a 

 dull yellow and red. Large series from every possible locality, with 

 exact data respecting habitat, must be studied before we can venture 

 on an opinion in the matter of cause and purpose. The varieties are 

 widely distributed, for, in addition to my own records, I have notes of 

 their appearance in Hungary, Scandinavia, and elsewhere. 



The girdle of Allurus, which commences on segment 22 and ends 

 on the 27th, is rather nearer the head than the tail. The latter portion 

 of the body is angular, and usually consists of about forty segments, 

 so that an entire, full grown worm should contain about seventy or 

 eighty rings. I have found as many as ninety segments on a large 

 specimen. The male pore may be easily detected on either side of 

 segment 13, running parallel with the rings. The lip does not per- 

 fectly bisect the first ring. As I do not intend to refer to internal 

 anatomy in these papers as a means of identification, I shall be con- 

 tent to direct the reader's attention to the details and references 

 supplied in my article, already quoted, where its distribution so far as 

 known last year is also detailed. 



I may properly close this paper with a brief systematic description 

 of the external characters of the " Square-tail " worm. 



Name, Alhirus tetraedrus (Eisen, 1870). Length one to two 

 inches. Colour usually a dirty brown, but variable. Normal num- 

 ber of segments 70 to 80, the girdle occupying 20 to 27. Male 

 pores on papillae, laterally on segment 13. Lip (prostomium) rounded 

 in front, delicate, ramified with blood vessels, only partially cutting 

 the first segment (peristomium). Hinder extremity angular with a 

 pair of setoe at each angle, about 40 segments behind the girdle. 

 SetK of three kinds, viz. : the ordinary bristles, penial setae on 

 segment 8, and small claws or spinets. First record for Essex, 

 December 5th, 1888, Rev. O. P. Cambridge, B.A., confirmed by Dr. 

 Benham and H. Friend. 



