1901.] or THE GENUS BENHAMIA. 191 



the genus Diehogaster (originally instituted by myself ^), which has 

 priority. This genus Bicliogaster was also extended so as to include 

 Microdrilus, Millsonia, and Balanta. The extended genus will 

 contain therefore at the present moment no less than 70 species. 

 If it can he avoided, it appears to me to be imdesirable to divide 

 families into such large genera. I do not for a moment deny that 

 the difference between the several types, which were distinct 

 enough at the time of their creation as genera, are through further 

 discovery rendered small. Nevertheless it appears to me to be 

 still possible to retain the genus Benhamia (which perhaps must 

 include Trigaster) for those Acanthodrilid worms in which the 

 male pores are quite independent at their orifice from the spermi- 

 ducal glands, and which in all cases (save only in Benhamia viridis) 

 open on to a segment (the xviiith) lying between those upon 

 which open the two pairs of spermiducal glands. But B. viridis 

 is not exceptional in the fact that the sperm-ducts are quite 

 independent at their orifice of the spermiducal glands, Benhamia 

 is, at least mainly, an African genus — tropical African. Some 

 38 species are confined to that continent, and two others have been 

 found in the Malay Archipelago as well, while a third has been met 

 with in many parts of the world. Four are, so far as we know at 

 present, confined to the Oriental region, while 9 (exclusive of the 

 species of the genus Trigaster) are Central- American and West- 

 Indian. It is held, and as I think rightly held, by Michaelsen 

 that the real home of the genus is tropical Africa, and that 

 there is a great possibility that the species not found within 

 that area have been accidentally transferred. As to the ease 

 with which this may have occurred there is plenty of evidence 

 which I need not recapitulate here. There are, as it appears 

 to me, two strong pieces of evidence in favour of the view that 

 it has occurred in the case of this particular genus, which are 

 these : — firstly, three species are common to Africa and to some 

 other part or parts of the globe : secondly, the species of the genus 

 Benhamia of Western Africa are different from those of Central 

 and Eastern Africa, Now migration across the continent must 

 ■ surely be an easier matter than migration so far as the Malay 

 archipelago ; we thus are forced to conclude that if so trifling a 

 barrier, comparatively speaking, as the breadth of equatorial Africa 

 has prevented the intermingling of western and eastern species, 

 the enormous tracts of land and sea which intervene between 

 Benhamia holaui in Africa and the same species in other parts of 

 the world must have been traversed by some other means than 

 unaided effort. 



(1) Benhamia moorii, n. sp. 



Mr. Moore has very kindly placed in my hands two specimens 

 of earthworms collected by him in Africa. One of these is well 

 preserved, and is a large and, as I believe, new species oi Benhamia, 



^ Quart. Jouvn. Micr. Sci. xxis. p. 251. 



