152 Wisconsin Academy of Sciences, Arts, and Letters. 
end than anywhere else, and is usually slightly bowed-in in 
the middle line. The middle of the appendage is slightly 
arched as seen laterally. There is some variation in the form 
of this structure. 
A peculiarity of the palpi is the nearly oblong form of the 
fourth segment; the fifth is small and forked. The whole limb 
resembles that of A. Birgei nov. spec. The first and second 
pairs of legs bear the usual stiff hairs and spines; their last 
joints are peculiar in being the longest and in bearing many 
fine short hairs. The third pair of legs have long fine hairs 
on the third, fourth and fifth joints. In the fourth pair of 
legs, all segments but the first and the last bear many long 
hairs; the process on the fourth is long and bears the usual 
bunch of hairs. 
The color is dull blue-green with indistinct flecks of brown 
as in A. glob at or. The entire length is 0.9 mm; the width, 
0.57 mm; the length of the appendage, 0.37 mm. 
Arrenurus securiformis Piersig. 
Fig. 4, a—c, PL XVIII. 
Arrenurus buccinator Piersig, 1894 (a) ; S. 414. 
Arrenurus securiformis Piersig, 1894 (b) ; S. 378. 
Arrenurus buccinator Kramer, 1895; S. 1-5, Fig. 1. 
Arrenurus festivus Koenike, 1895; S. 378, Fig. 2. 
Arrenurus festivus Koenike, 1896; S. 213. 
Arrenurus securiformis Piersig, 1896; S. 58. 
Arrenurus securiformis Piersig, 1897; S. 282-84, Fig. 75. 
Arrenurus securiformis Piersig, 1901; S. 83. 
Fine individuals found in a small pond near Xobska Light, 
Wood’s Hole, Mass., in August, 1899, are clearly to be identi¬ 
fied as A. securiformis Piersig. The form of the appendage 
is the most distinguishing feature. The prominent hump near 
the posterior end has a semicircular form (fig. 4, a and c, 
H 1 ). Just back of it are two little projections close together, 
and lying back and between them is a very small conical pro¬ 
jection (E). In the slight indentation at the eixtreme end is 
