Marshall—A New- Arrenurus. 
523 
pression. There are a number of hairs on this part of the 
appendage, as shown by the figures. In general these structures 
agree with those of Koenike’s detailed figures. The body is 
moderately elevated inside the dorsal line, though not as much 
so as Piersig shows. The dorsal line runs over on the append¬ 
age and is unclosed. The genital areas form scarcely percepti¬ 
ble rolls on the dorsal side. At their ends are four hairs on 
each side. The epimera are of the usual form, and the legs pre¬ 
sent no striking peculiarities distinct from other Arrenurus 
males. 
Through the kindness of Dr. C. F. George, identified speci¬ 
mens of A. caudatus from England were obtained for compari¬ 
son. The Wisconsin form was found to differ from these in the 
same details that it differed from the descriptions of the German 
hydraehnologists. From the same source were received also 
specimens of A. globator Miill., A. cylindratus Piers., and A. 
securiformis Pier. (= A. festivus Koen.). Here again, in sev¬ 
eral details of structure, they did not agree with the forms 
already identified by the author (1903). However, the differ¬ 
ences have not seemed great enough, without further compari¬ 
son with European forms, to justify the formation of four new 
species. 
Arrenurus Morrisoni nov. spec. 
Plate XL, Figs. 2a—-2d. 
This new species is represented in the author’s collection by 
only one individual. It was found July 30, 1903, in Morri¬ 
son’s Pond, near the Little McKinzie Hiver in Washburn 
County, Wisconsin. This pond is perhaps one-fourth of a mile 
long, and nearly filled up with water-lilies and other plants. 
Collections were made at various points; but A. Morrisoni and 
A. Birgei Mar., with one female unidentified, were the only 
Arrenuri found, and of these but a single individual each. 
The new form was not examined until after it had been a few 
days in Koenike’s preserving fluid; it had then a pale yellow¬ 
ish hue, probably not differing much from the color in the fresh 
specimen. It measured 1.23 mm. in length and 0.68 mm. in 
width. Its most striking feature is the appendage which is 
nearly two-thirds as long as the body. It is rather low, mod¬ 
erately constricted at the base; then it rounds out considerably 
t. 
