A NEW GENUS OP OLIGOCH^TA. 469 



segments will in all probability be found to bave a median area 

 upon wbich there is no great modification of the epidermis. 

 This area is of course bounded laterally by the genital ridges. 

 It seems, therefore, that the clitellum of Deodrilus is consti- 

 tuted upon the same plan as that of Acanthodrilus. 



Dr. Rosa has made some use, in his scheme of classification 

 of earthworms, of the form of clitellum, which he terms saddle- 

 shaped ("clitello a sello'^), or complete (^'cingulo completo"), 

 admitting that Acanthodrilus offers an intermediate con- 

 dition. 



The fact is that it is not possible to classify the various modi- 

 fications of the clitellum in this way. 



There is a considerable series of gradations which renders it 

 impossible to make a fixed demarcation between the difi'erent 

 forms of clitellum. To commence at one extreme, we have 

 species of Lumbricus and Allolobophora with a distinc- 

 tively saddle-shaped clitellum : in these forms the glandular 

 modified epidermis is only to be found on the dorsal and lateral 

 regions of the clitellum ; ventrally there is a wide space of equal 

 diameter throughout, which has no trace of glandular tissue. 



In such a form as Rhinodrilus Gulielmi the clitellum 

 is divisible into two regions : in the last six segments of which 

 it is composed the glandular substance is arranged quite as in 

 Lumbricus; but in the first four the ventral area is en- 

 croached upon by the glandular tissue, though it is not 

 completely invaded. 



In Urochseta the clitellum is constituted in a way quite 

 resembling that of Rhinodrilus, but the anterior bare ventral 

 space appears if anything to be somewhat narrower. 



In Deodrilus (which, as will be shown later, has points of 

 affinity with Rhinodrilus) the anterior part of the clitellum 

 is completely developed — extends all round the body — but the 

 greater part is still only laterally developed. 



Acanthodrilus has a clitellum inwhich the anterior portion 

 is at least as great as, and may be greater than, the hiuder 

 portion, which still retains its saddle-shaped character. 



Finally, we have such a form as Perionyx, in which the 



