218 robert h. wolcott: 



females. There is usually a tinge of blue in the Michigan 

 specimens, lacking in those from Nebraska. 



5. Atax abnormipes Wolcott. 



Atax abnormipes Wolcott, '98; 280. 



Among the species to be considered in this paper are two which are 

 quite different from all others, which bear a very close resemblance to 

 each other and which are yet clearly distinct. They are both peculiar in 

 the possession by the males of a highly modified fourth pair of legs, while 

 the females present no marked structural peculiarity. The first of these 

 is Atax abnormipes. It is one of the smaller species, the females aver- 

 aging about 0.7 mm., the males about 0.55 mm. The body of the former 

 is about one-sixth longer than broad, somewhat broader posteriorly and 

 so slightly pyriform in shape and evenly rounded at both ends. In pro- 

 file it is about two-thirds as high as long, flattened dorsally in the center, 

 the outline descending abruptly at either end. The surface of the body is 

 marked by lines dividing it into minute hexagonal areas, appearing 

 facetted. The male is decidedly pyriform, with a breadth equal to four- 

 fifths its length, the average of a number of specimens being 0.445 mm. 

 and 0.56 mm. respectively. The body is smoothly rounded' anteriorly, 

 but deeply emarginate posteriorly. 



Eyes very large, in the male measured, 0.143 mm. apart. Each lens 

 nearly circular, the anterior a little the larger. 



Maxillary shield, — Comparatively broad, the sides anteriorly nearly 

 parallel, with the anterior lateral angles diverging. The ancoral process 

 very broad with a width at the tip of over half the extreme breadth of the 

 whole, inconspicuously hooked and with sides which from the tip di- 

 verge at once to the posterior lateral angles, which thus instead of ap- 

 pearing posterior, seem like projecting angles in the middle of each side. 



Mandibles. — The basal segment is broadly rectangular, nearly as 

 broad as long, slightly narrowed anteriorly, the dorsal posterior angle 

 rounded, the ventral angle produced for attachment of muscles. Distal 

 segment comparatively large, the claw rather heavy, slightly curved and 

 quite blunt. Patch of oblique striae near its base sharply limited and 

 with a broadly elliptical outline. 



Palpi.— Whole palpus slender and somewhat less than one-half the 

 length of the body. Basal segment short, while 2 is of moderate length, 

 relatively thicker than the rest, and convex along both extensor and flexor 

 margins, the convexity of the former the greater; on the outer side are two 

 long, tapering, slightly curved spines toward the extensor margin; on the 

 inner surface one, similar to the others, in the middle, and a second close 

 to the distal margin. 3, somewhat narrower than 2 and proportionately 

 ong, though hardly as long as broad; flexor margin nearly straight; 

 extensor margin convex; a spine at the proximal margin of outer surface, 

 nearer the extensor side, and another at the distal margin on the inner 

 side. 4, long and slender, narrower than 3, about three times as long as 

 thick and slightly tapering toward the end; paired papillae on the flexor 



