158 Wisconsin 'Academy of Sciences, Arts, and Letters. 
Arrenurus conicus Piersig. 
Pig. 9, a—d, PL XVIII. 
Arrenurus spec. Piersig, 1893; S. 311. 
Arrenurus conicus Piersig, 1894 (a) ; S. 413. 
Arrenurus conicus Piersig, 1897; S. 291-294, Pig. 73. 
Arrenurus conicus Piersig, 1901; S. 86-87, Pig, 19-20. 
Only one individual belonging to this species was found, and 
this was in Lake Wingra, August 6th, 1902. It was readly 
identified with Piersig’s form! by the broad, stout appendage 
with constricted base and very narrow end. But instead of 
four little scallops, it ended in three', the middle one longest. 
As seen from the side, the region inside of the dorsal line is 
depressed, and the appendage is higher than shown by Piersig. 
On the dorsal side of the appendage were found two little oval, 
light colored spots just before the lateral constriction near the 
end (Pig. 9, a, d). The last segment of the fourth leg is 
slightly curved; the fourth bears the usual process. The length 
was found to be 1.16 mm.; the width, 0.7 man. 
Arrenurus Birgei nov. spec. 
Pig. 10, Or-f, Pis. XVI—XVII. 
This form with its moderately long appendage stands be¬ 
tween the forms like A. glob at or with this organ enormously 
developed, and species like A. oblongus Piersig and A. truncar 
iellus Muller, where the short appendage and body are not 
sharply marked off from each other. However, the appendage 
in A. Birgei though short, is much narrower than the body and 
clearly marked oh from! it in the dorsal and ventral aspects. 
The body is rounded and bowed in a little between the eyes. 
The middle lateral walls are nearly parallel as seen dorsally. 
The body is moderately elevated, highest in the middle, where 
it is nearly flat. The area of the dorsal shield is slightly 
broader than long and is a little depressed. Prom here on 
the body slopes gradually to the posterior end of the appen¬ 
dage, the only interruptions being a rounded hump just be¬ 
fore the end of the appendage, and a pair of low humps in 
