146 Wisconsin Academy of Sciences, Arts, and Letters. 
a short appendage as wide as the body; at the end of it is a 
deep incision in which lies a small petiole. Arrenurus forpica- 
tus Neuman belongs to the group. The third subgenus, Mega*- 
turns, includes forms having a very dong appendage, but the 
petiole is absent, or represented by a very small transparent 
projection. The species described in this paper all belong to- 
this subgenus. 
Thor erects still a fourth subgenus, Truncaturus, to include 
species which like Arrenurus truncatellus (Muller), A. Knan- 
thei Koenikei, A. oblongus Piersig, have neither petiole nor dis¬ 
tinct body appendage, and so ap" "ach the females in form. 
This subgenus represents the least differentiated branch of the 
genus. 
The appendage, the petiole, and the humps on the appendage 
and posterior part of the body which contain large glands and 
their openings, are probably all sexual characters. The 
area containing the openings of the genital organs is very simi¬ 
lar in all species and. both sexes of the Arrenuri. The open¬ 
ings are small slits; on the ventral side of the body near the 
end, and are largest in the female. On each side is a. semi¬ 
circular plate in the female 1 , and a narrow rim in the male; 
from these run wing-shaped lateral areas, the so-called “Napf- 
platten,” large and broad in the female, narrow and long in 
the male, and often forming characteristic rolls between body 
and appendage. 
In all Arrenuri the epimera, or ventral leg plates, are in 
three groups, and in the different species show no very strik¬ 
ing differences. The palpi are claw-like. The legs bear long 
fine hairs and short bristles. The fourth pair are longest, and 
the fourth segment in the mules bears a short process whose 
use is not clear. Besides having a probable use in sexual in¬ 
tercourse in the male, they are used somewhat differently than 
the other appendages in both sexes. They are often seen bent 
up close to the body and they have ai great range of movement. 
They are often jerked violently backward, while the anterior 
three pairs are used as walking legs or oars. The last pair are 
sometimes used to remove debris from the body. 
Arrenuri were collected at various times from the first of 
