NORTH AMERICAN SPECIES OF THE GENUS ATAX 205 



all measurements of legs which follow the claw is not included 

 in the total. For the sake of brevity the legs and the epimera 

 corresponding are frequently referred to by Roman numerals 

 and the segments of the legs and palpi are numbered from the 

 base outward, using Arabic numerals; thus "III 3" refers to 

 the third segment of the third pair of legs, and "Palpus 5" to 

 the distal segment of the palpus. 



I 



DESCRIPTION OF SPECIES. 

 I. Atax crassipes (Muller). 



Hydrachna crassipes Muller, 1776; 189, no. 2254: id., 1781; XLI, PI. 

 IV, f. 1, 2. 



Trombidium crassipes Fabricius, 1792; II, 400. 



Atax crassipes Fabricius, 05; 366: Koch, 35; 7. 21: id., 37; III, 8, PL 

 I, f. 1. 



Atax elegans Koch, 35; 7, 12. 



Atax truncatus Koch, 35; 7, 22. 



Atax albidus Koch, 35; 7, 23. 



Atax confluens Koch, 35; 7, 24 (nymph). 



Atax truncatellus Koch, 35; 37, 17 (nymph). 



Hydrachna crassipes Walckenaer and Gervais, 44; III, 197. 



Atax crassipes Bruzelius, 54; PL I, f. 1-4: Claparede, 68; 471: Kramer, 

 75; 293: Lebert, 79; 368, PL XI, f. 10, 10a; Neuman, 80; 21, PL I, f. 1: 

 Koenike, 81a; 627: id., 81b; 356: Haller, 81a; 76: Berlese, 82; fasc. IV, no. 

 7: Krendowsky, 85; 55: Barrois and Moniez, 87; 5: Piersig, 94b; 214: 

 Koenike, 95a; 139: id., 96a; 232: Piersig, 96; 40: id., 97; Lief. I, 52, 

 PL III, f. 5, a— h. 



Atax crassipes is noteworthy among the species of this genus, for the 

 great length of its legs, which cover a greater area than those of any other 

 species, though its body is smaller than many others. The body of the male 

 varies in length from 0.5 to 0.7 mm., while the female is from 0.7 to 0.9 mm. 

 and even 1.1 or 1.2 mm. long. Its form is broadly oval, with the larger 

 end of the oval anteriad and evenly rounded, the smaller end posteriad 

 and truncate, projecting nipple -like papillae at either side giving this end 

 the appearance of having been cut squarely off. The greatest breadth is 

 about opposite the third epimeron. The nipple-like papillae exhibit 

 varying degrees of prominence and Piersig describes a muscle which serves 

 as a retractor and by which they may be made to completely disappear. 



The double eyes are very large, blackish in color, close to the margin 

 and moderately distant from each other, in a specimen 0.618 mm. long 

 being 0.184 mm. apart. The anterior portion of each eye is larger and 

 nearly twice as large as the posterior. 



