CH. i] ACANTHODRILIDiE. 65 



Australian region is a matter of moment, and recalls other 

 distributional facts. 



Not less interesting are the distributional facts con- 

 cerning the Acanthodrilidae. This family is divisible 

 into the following genera: — Acarvthodrilus, Benhamia, 

 Octochcetus, Diplocardia, Deinodrilus, Kerria and Plagio- 

 chceta. The family itself is separable from all other 

 earthworms by the fact that, with the single exception 

 of the species Acanthodrilus monocystis, formerly placed 

 by me in a distinct genus Neodrilus, there are two pairs 

 of spermiducal glands, which have not, as they have in 

 nearly all other earthworms, a near connection with the 

 sperm ducts, but open actually on to different segments 

 from them; these segments are XVII. and XIX. the 

 sperm ducts reaching the exterior by a pore situated 

 upon segment XVIII. The two pairs of glands as well as 

 their position are the distinguishing features of the family. 

 The further division of the family into genera is in some 

 respects not an altogether easy task. Deinodrilus is to be 

 at once distinguished by the fact that it has the unique 

 character of having twelve setae in each segment of the 

 body; Plagiochceta has a larger number still, as in the 

 Perichaetidae ; but the genus could not be confounded with 

 a Perichaetid by reason of the fact that these setae are 

 disposed in pairs. Benhamia, Acanthodrilus and Octo- 

 chcetus are with more difficulty separable; Benhamia and 

 Octochcetus have the excretory organs on the same plan 

 as those of the majority of the Perichaetidae ; they are 

 extremely numerous in each segment of the body and 

 open on to the exterior by very numerous pores on each 

 B. z. 5 



