V] RELATIVE FREQUENCY 93 



instance Octochaetus is well known from New Zealand, 

 and, not occurring in the intermediate tracts, is again 

 met with in India. Hoplocliaetella is believed by 

 Michaelsen to present us with another precisely 

 similar instance. Then also the genera Woodwardia 

 and Notoscolex are to be found in Australia and again 

 (absent from the immense tract lying in between) 

 in Ceylon. Megascolex has much the same range, 

 showing also this marked and remarkable discon- 

 tinuity. Stranger still, perhaps, is the range of 

 Plutelliis and MegascoUdes, of which the former, 

 chiefly found in Australia and Tasmania, not only 

 extends its habitat to Ceylon but also to North 

 America; it is there represented by Eisen's species 

 Argdophihis marmoratus, referred by him, and not 

 unnaturally, to a distinct genus, but placed by 

 Michaelsen in Plidellus. MegascoUdes is Australian 

 and from the North Island of New Zealand, where 

 its species were regarded by Benham as of a distinct 

 genus, Tolea. There is also one form, MegascoUdes 

 aiaericanus, in the western region of North America. 

 The two genera Yagansia and Chi/ofa, closely 

 related to Notlodrdas, have a range which is short 

 of that of Notiodtilns, and we shall see later that 

 there are i-easons for regarding these genera as 

 derived from Notlodr'dns. They are met with only 

 in the south of South xVnierica, iind in the Cape of 

 Good Hope region. 



