i 9 2 SCIENCE PROGRESS. 



As to other distributional facts and theories, it is 

 probable that I have underestimated in my Monograph the 

 distinctness of the Palaearctic and the Nearctic regions of 

 Mr. Sclater. I was disposed to unite them into one Hol- 

 arctic as Professor Newton has called it. Further investi- 

 gations have tended to emphasise the justice of separating 

 these two regions. This evidence has been mainly collected 

 by the industry of Dr. Gustav Eisen, of San Francisco ; 

 but others whose names and memoirs will be found quoted 

 in the list of literature at the end of this article have added 

 details of importance. The North American continent is 

 inhabited by a fair number of peculiar genera, of which 

 Diplocardia, originally described some years since by 

 Garman, has four species (partly referred to the undoubtedly 

 synonymous genus Geodrilus) ; there are also peculiar to 

 this region Phoenicodrilus, nearly related to the central 

 and South America Ocuerodrilus, and Sparganophilus ; of 

 this latter genus the original species was found by 

 Benham in the Thames ; but as there are half a dozen 

 American species it seems likely that its occurrence in 

 England is a case of importation. Bimastos is a genus 

 perhaps justly separable from Allolobophora, from which it 

 chiefly differs in the large size (for a Lumbricid) of the 

 glandular sac in which the efferent male ducts terminate. 

 Besides these peculiar genera are a few species of the 

 Central and South American genera Ocuerodrilus and 

 Kerria, and of the almost world-wide Benhamia. Aleodrilus 

 is an Acanthodrilid that Eisen is disposed to separate from 

 Diplocardia ; two species of Acanthodrilus complete the 

 list of non-European inhabitants of the North American 

 Continent. But in addition to these are a number of Allolo- 

 bophora and Lumbricus — the characteristic forms ol the 

 Palaearctic region — two or three of which are, however, so 

 far as our present knowledge goes peculiar to North 

 America. These facts perhaps justify the retention of 

 the Nearctic region, and they are perhaps also significant 

 in that the peculiar forms are western in range — a possible 

 indication of their approaching extirpation by European 

 species introduced by commerce. 



