384 OLIGOCHAETA 



(in most of the species), but the calciferous glands have been 

 reduced to a single pair, which lie in the ninth segment. The 

 latter character is also found in the Acanthodrilid Kerria, which 

 has been associated with the above named. Gordiodrilus has the 

 peculiarity that there are, as in Acanthodrilids, two pairs of 

 tubular spermiducal glands. 



Fam. 11. Acanthoclrilidae} This family is only with diffi- 

 culty to be distinguished from the last. The following definition 

 applies to all the members of the family with one exception, and 

 does not apply to any Cryptodrilid with, so far as is known, one 

 exception only. There are two pairs of spermiducal glands, 

 opening upon the segments in front of and behind that which 

 bears the apertures of the sperm-ducts. 



The one exception to this definition is the species Acanthodrilus 

 monocystis, which I formerly placed in a distinct genus, Neodrilus. 

 Microscolex modestus is the exception among the Cryptodrilidae ; 

 in that worm the male pores are upon the segment which follows 

 that upon which the spermiducal glands open. The Acantho- 

 drilidae show a considerable range of structural variation. This 

 enables them to be separated into several well-marked genera. The 

 type genus Acanthodrilus has a pair of nephridia in each segment. 

 It contains thirty-five species, which are all from the southern 

 hemisphere. These species show but little variation among 

 themselves. Benhamia is a genus that differs from Acanthodrilus 

 in the fact that the nephridia are of the complex type, so often 

 met with in earthworms with many external pores. The seg- 

 ment that bears the male pores is entirely without any traces of 

 the ventral chaetae. Here again there are a large number of 

 species which are nearly confined to the continent of Africa. Dr. 

 Michaelsen is indeed of opinion that the few species found in the 

 East Indies and America are accidental importations. I have 

 proposed to separate some of the New Zealand Acanthodrilids 

 into a distinct genus, Octochaetus, which is somewhat intermediate 

 between Acanthodrilus and Benhamia. They have multiple 

 nephridia, but only a single gizzard. Plagiochaeta of Benham, 

 from New Zealand, is in any case clearly a distinct form. It is 

 mainly to be distinguished by the numerous chaetae in each 

 segment. Trigaster Benham, is West Indian. Beinodrilus (New 



1 Beddard, P. Z. S. 1885 and 1895, for Antarctic Acanthodrilids ; Michaelsen, in 

 Jahrb. Hamburg. Anst. 1888-95, for Benhamia. 



