It will appear therefore that many and considerable differences divide _Pontoscolex_ from _Notiodrilus_ and indeed from all of the Megascolecidae whose structure has been touched upon in the foregoing pages. The most important of these are the ornamented setae and their arrangement and the modification of the setae upon the clitellum: the absence of diverticula to the spermathecae: the absence of terminal glands associated with the male ducts. Although taken in their entirety these characters are distinctive of the American Geoscolecidae (sub-family Geoscolecinae), there is no one of them which is not to be found in some Megascolecid. Thus the subgenus _Ilyogenia_ (of _Ocnerodrilus_) has sometimes no spermiducal glands: the genus _Perionyx_ has spermathecae without diverticula in some species, and other genera of Megascolecinae are in a like condition. The setae of _Dichogaster_ are sometimes ornamented, while in _Pheretima houlleti_ the clitellar setae are different from those upon the other segments. We can in fact only define the family Geoscolecidae by an assemblage of characters which are mainly these: dorsal pores absent, only a few in the neck region being occasionally present; setae generally ornamented, those of the clitellum being larger and more marked than the others; spermathecae without diverticula; often instead of a pair of those pouches in the segment a large number of very small sacs, as in _Microchaeta_, _Kynotus_. Sperm ducts without terminal glandular or muscular sac, except in a few cases; setae always eight in a segment except in the genus _Periscolex_ which has acquired the 'perichaetous' condition. The range of variation shown in the anatomy of the Geoscolecidae will be best taken in connection with the several sub-families into which it has been subdivided. In the first of these, the Geoscolecinae, no great differences divide the genera from that selected as the type, viz. _Pontoscolex_. The long sperm sacs attain to an extraordinary length in _Trichochaeta_ (or _Hesperoscolex_) where the single pair extends through no less than 109 segments. Though as a general rule the sperm ducts open directly on to the exterior they do so through the intermediary of a large pouch in _Glossoscolex_ (= _Titanus_). In _Onychochaeta_ the setae on the last segments of the body are very much enlarged and thus form a more effective means of holding on to the soil than is possessed by other species.