1302 Wisconsin Academy of Sciences, Arts, and Letters . 
middle of the appendix. In addition, the area inside of the dor¬ 
sal line is depressed, not elevated as in the related species; and in 
the small structures on the end of the appendix on the dorsal 
side the two species do not agree. The palpus is characterized 
by the great length of the saber-like hair on the fourth joint, and 
by the presence of a small bunch of hairs on the inner side of the 
second. 
But one specimen is known; this was found in Sebago Lake, 
Maine, Aug. 4, 1911. The entire length of the body is 1,28 mm.; 
the color is orange green. 
Arrhenusus crenellatus Mar. 
(PL I, fig. 9-11) 
In collections from Sebago Lake, Maine (Aug. 4, 1911), there 
were found six males of this species, and one female which exam¬ 
ination of the palpi proved to be A. crennellatus also. The epi- 
mera of the female are like those of the male. The wing-shaped 
genital areas completely enclose the genital plates as shown in 
the figure. The dorsal enclosed area is an oval of the usual form. 
The second joint of the palpus of this species has an area of fine 
hairs; the former description of these hairs (1908) as blade-like 
is now found to be an error. The color of the preserved female is 
dull yellow; the length of the body is 0.87 mm. 
Notes on the Arrhenuri 
Collections made since 1910 (the last published notes on the 
genus), together with collections from the East very kindly con¬ 
tributed by Mr. A. A. Doolittle of Washington, D. C., have added 
one new species to the genus and the female of another species, 
as already described, while the range of still other species has 
been extended. Some details of structure not given in earlier 
studies are given in the plates, and the list of species is given be¬ 
low. 
In pools at Epworth eight, near Ludington, Michigan, were 
found 
A. scutulatus Mar. (PL II, fig. 17, 18) 
A. infundibular is Mar. (PL II, fig. 19) 
A. scutuliformis, Mar., female, (PL II, fig. 20.) 
A. pseudocylindratus Piers. 
