STUDIES ON EARTHWORMS. 217 
lus, Digaster, Pontoscolex, Pontodrilus, Plutellus, 
Perionyx, Megascolex, and Pleurocheta. 
4, The group Aclitelliani is formed for the genus M oni- 
ligaster, which has no clitellum, although the only specimen 
studied had its genital organs fully mature, and, indeed, more 
complicated than any other form. 
The habitat of these forms is given later on, in Section IT, 
where the names, &c., of all known Earthworms will be found. 
IJ. PrReviousLy DESCRIBED GENERA. 
In this section I shall mention, in chronological order, and 
briefly notice, all Earthworms whose description I have been 
able to find. In the case of the genus Lumbricus [ have 
placed all the species together at the end of this section. The 
anatomy of the genus Lumbricus is sufficiently well known 
through the works of d’Udekem (16), Lankester (48), Clapa- 
réde (11), and others, so that I will refer only to Eisen’s work 
(15), where he subdivides the genus into three subgenera: 
1, Lumbricus, with the male pore in somite xv, and the 
prostomium embedded deeply in the first somite. 
2. Allolobophora, with the male pore in somite xv, and 
the prostomium embedded less deeply in the first somite; this 
includes Dendrobena, which Eisen at first separated, but 
now includes. 
3. Allurus, with the male pore in somite xu. 
It seems to me that the character drawn from the prostomium 
is scarcely of generic importance, since forms otherwise similar 
have this difference (e.g. Lumbricus agricola and L. oli- 
dus), but the variation in the positions of the male pore is a 
good sub-generic character. 
The earliest genus additional to Lumbricus was Hypo- 
geon, formed by Savigny (1) in 1820, but, as in so many of 
these earlier genera, a very poor description is given, and only 
of external characters. Hypogzon has nine long setz in each 
somite, one being in the dorsal mid-line; these sete do not 
alternate in consecutive somites. 
