1891.) Some Recent Papers on Earthworms. 7 
MıcropriLI (Water Worms). 
No capillary network of blood-vessels on nephridia ; small 
size, thin, transparent body wall; setz always in four groups 
per somite ; prostomium not separated from peristomium by a 
groove. Contains families Discodrilide, Enchytreide, Phre- 
oryctidz, and Lumbriculide. 
MEGADRILI (Earth Worms). 
Large forms from one inch to six feet in length. Body 
wall thick and opaque; prostomium (when present) separated 
from peristomium by a groove; capillary network of blood- 
vessels on the nephridia; clitellum always occupying more 
than two somites. These are divided into PLECTONEPHRICA, 
with the nephridia in the form of delicate tubules in 
each somite, uniting to form a network, with more or less 
numerous external apertures; and MEGANEPHRICA, with the ex- 
cretory network absent, replaced by a pair (rarely two pairs) of 
large nephridia in each somite. The members of each division 
are given below, the genera known to occur in the United States 
being given in italics . 
PLECTONEPHRICA. 
Family TYPHÆIDÆ ; genera Typhzus, Megascolides, Crypto- 
drilus, Didymogaster, Perissogaster, Dichogaster, Digaster. 
Family ACANTHODRILIDZ; genera Acanthodrilus, Trigaster, 
Dinodrilus, Neodrilus, Diplocardia. 
Family PERICHÆTIDÆ ; genus Pericheta (including Mega- 
scolex). 
MEGANEPHRICA. 
Family MoNILIGASTRIDÆ ; genus Moniligaster. 
Family EUDRILIDÆ ; genera Eudrilus, Teleudrilus, Pontodrilus, 
Photodrilus, iici Rhododrilus, Plutellus, Stuhlmannia, 
Hyperiodrilus. 
Family PERIONYCHIDÆ ; genus Perionyx. 
Family GEoscoLECIDÆ ; genera Geoscolex, Urochzta, Dia- 
Cheta.” > . 
