8 The American Naturalist. LJanuary, 4 
Family RHINODRILIDÆ; genera Rhinodrilus, Microcheta, — 
Urobenus, Hormogaster, Brachydrilus. 
Family LUMBRICIDÆ ; genera Lumbricus, Allolobophora, Crio- 
drilus, Allurus. 
Besides the above, Benham includes four genera of uncertain 
position, viz., Helodrilus, Echinodrilus, Antæus, and Eisenia. 
The genera of Megadrili recognized by Benham may be sepa- 
rated by the following key, modified only in method of arrange- 
ment from that given by him : 
A, Setæ 16 to 80, or more, in a ring. 
a, Male pores far apart; small tufts of ne- 
phridia ; Pericheta. 
aa, Male pores very close together; large 
nephridia ; Pertonyx. 
AA, Twelve sete on somite; clitellum on somites 
14-16; Dinodrilus. 
AAA, Eight sete on somite. 
a, Sete alternate in consecutive somites 
throughout body; male pore on somite 
22; Diacheta. 
_ aa, Sete alternate only posteriorly; male 
pore 20-21;° clitellum on somites 14-22 ; Urocheta. 
aaa, Setz in rows, not alternating. 
8, Male pores 10-11, or 11-12; Moniligaster. — 
PP, Male pores on somite 13; Ailurus. — 
888, Male pores on somite 15. 
y, Prostomium dovetailed completely 
into peristomium ; Lumbricus. — 
rr, Dovetailed incompletely ; Allolobophora. 
777, Not dovetailed ; Criodrilus. — 
ABBR, Male pores 15-16; Hormogaster. — 
88888, Male pores on somite 17. 
7, Clitellum on somites 14-17, 
ð, Sete separate ; Rhododrilus. — 
00, Setz in couples. 
© Between somites 20 and 2r. 
E€, One pair of sperm sacs; Typhaeus. 
