154 Wisconsin A cademy of Sciences, Arts , and Letters. 
The three anterior pairs of legs are like those of A. secnri- 
formis. The fourth legs are characterized by the presence of 
many little thorn-like bristles on the fonrth and fifth joints, 
and by the shortness of the last two joints. The longest and 
most numerous hairs are on the fifth joint, and the fonrth has 
a prominent process bearing a small bunch of stiff curved hairs. 
Five males of A. cardiacus were found in Goose Pond, 
Adams County, a small, shallow, stagnant body of water filled 
up with water plants. The color of the specimens was deep 
indigo blue with lighter brown patches on the anterior end 
of the body and the middle of the appendage. 
The length is 1.3 mm; width, 0.66 mm; appendage, 0.5 
mm; first leg, 0.78 mm; fourth leg, 1.05 mm. 
A few females were found. They have the usual form; and 
structure of female Arrenuri. The body is ovate with slight 
indentations. The dorsal shield is oval and reaches nearly to 
the posterior edge of the body. The epimera, are like those in 
the males. The genital area, is large and of nearly uniform 
width and extends nearly straight out. There are numerous 
hairs as shown in Fig. 5, g and h. The color is the same as 
in the male. The length of the body is 1.06 mm; the width, 
0.94. 
Arrenurus parallellatus nov. spec. 
Fig. 6, a—e, Pis. XVI—XVIII. 
The name of this new species is suggested by the form of 
the appendage, the sides of which are nearly parallel. The 
and has two low humps on each side projecting back equally 
(Fig. 6, a and c, H, 1 H 2 ). In the middle line is a deep rounded 
bay, narrowest at the mouth* into which projects a little fing¬ 
er-like process curved up dors ally (P). In a lateral view of 
the animal it can sometimes be seen through the semi-trans¬ 
parent rounded corners of the appendage, like the figure given 
by Piersig for the petiole of A. globator (Deut. Hydrach., fig. 
72, e). This structure may represent a petiole here. Just 
anterior to it lies a pair of little projections rising each from 
the summit of a little hump, the points of which turn outward 
