460 OLIGOCHAETA 



glands. We now know that precisely the same separation occurs in M. modestus. 

 It is not, therefore, requisite to do more than merely mention the fact that Eisen (16), 

 in ignorance of the condition obtaining in M. modestus, resuscitated my genus 

 Rhododrilus. The last-mentioned authority has founded a third genus Deltania. 

 This genus, which contains three species from California, is distinguished from 

 Microscolex by the fact that the ventral setae in the neighbourhood of the male 

 pores converge towards each other. This condition had been before described in 

 other species of Microscolex, which ErsEN accordingly referred to Deltania. Since 

 Eisen proposed this division nine new species of the genus have been studied by 

 myself from South America. If it is necessary to subdivide Microscolex, these new 

 species perhaps offer rather better characters. All of them differ from M. modestus, 

 &c., in having but a single pair of male gonads instead of two pairs. As some have 

 strictly paired setae instead of the eight rows formerly considered distinctive of both 

 Microscolex and Deltania, the approximation of the ventral setae to each other on 

 some of the genital segments loses its importance. Were these species the only 

 species of the genus to be found in South America I should be inclined to regard 

 the single testes and sperm-ducts to be a structural character requiring recognition 

 by generic separation. As, however, both M. dubius and M. modestus appear to be 

 indigenous inhabitants of the same part of the world this division seems to be less 

 necessary. As it is unaccompanied by any other character which is equally distinctive, 

 I prefer to leave the genus Microscolex undivided. The genus is quite easily definable 

 as will be seen from the above definition. The eighteen species are of very varied 

 sizes ; at one extreme we have Michaels en's ' Gryptodrilus spatulifer,' which I cannot 

 separate from the genus. At the other extreme there are specimens of M. modestus, 

 only 1 6mm. long, and these are among the smallest of earthworms. The head-quarters 

 of the genus is evidently in America, where fourteen of the species occur ; of these 

 only two, viz. M. modestus and M. dubius, occur outside this region. Nine are 

 absolutely confined to South America, to the more temperate regions of that continent. 

 The following is a list of the species : — 



(i) M. modestus, RosA, Italy; Argentine. 



(2) M. dubius (Fletcher), Australia ; Argentine. 



(3) M. algeriensis, F. E. B., Algeria. » 



(4) M. poultoni, F. E. B., TenerifFe. 



(5) M. minutus, F. E. B., New Zealand. 



(6) M. novae-zelandiae, F. E. B., New Zealand. 



(7) M. spatulifer (Mich.), South America. 



