NORTH AMERICAN SPECIES OF THE GENUS ATAX 231 



acetabula smaller and more closely crowded toward the middle 

 of either side. 



Specimens were received from Prof. Kelly and Mr. Bicker 

 collected in U. plicatus at Havana, Ills. 



10. ATAX ARCUATA WOLCOTT. 



Atax arcuata Wolcott, 98; 284. 



A species equal in size to A. fossulatvs and A. ypsilophorus, between 

 which it appears to occupy an intermediate position, having resemblances to 

 both, but quite distinct from either. It is especially characterized by the 

 form of the legs, the distal segments of which are so strongly curved as 

 to suggest the name bestowed upon it. 



It is of the same elongated elliptical form which characterizes the re- 

 lated species, very slightly broader posteriorly, and with both anterior 

 and posterior margins evenly rounded. 



Eyes very small and lenses nearly equal. In the male specimen 

 measured the two were 0.301 mm. apart. 



Maxillary shield similar to that of A. ypsilophorus, except that the an- 

 coral process is not so long, and the lateral margins perhaps a little less 

 divergent anteriorly. 



Mandibles of the same form as in that species except that a concavity 

 is present in the posterior margin toward the ventral angle, whereas in 

 A. ypsilophorus the margin is nearly straight. 



Palpi also very similar to those of A. ypsilophorus, though varying 

 somewhat in the direction of those of A. fossulatus. 1, as heavy as in the 

 former species, but 3 relatively less thick, and 4, instead of tapering, 

 nearly as thick at its distal as at its proximal end, the ventral papillae 

 being more prominent. Distal segment slenderer and longer than in A. 

 ypsilophorus and the claws at the tip relatively smaller. 



Epimera. — Anterior groups narrower toward the median line and 

 more nearly triangular than in either A. ypsilophorus or A. fossulatus. 

 Posterior group much shorter than in either and inner margin distinctly 

 shorter than the outer, with both anterior and posterior inner angles very 

 much rounded, especially the latter, which causes the epimera of the two 

 sides to appear widely divergent posteriorly. Space between the two 

 groups of epimera on each side very wide. 



Legs very long, especially in the male, and similar to those of A. fos- 

 sulatus in that I is very markedly thicker than the rest and in that the 

 successive segments of each leg are distinctly slenderer than the one 

 next the body and give an evident tapering appearance. They are, how- 

 ever, relatively slender. Ill is a trifle longer than II, all but I exceed the 

 body in length, and IV is over half as long again. Of the segments, 5 is in 

 all legs unusually long and 6 abnormally short. The legs are less plenti- 

 fully supplied with spines than are those of either of the other two species 

 and the spines are rather weak. The legs are especially characterized by 

 the curved form of the terminal segment, the curvature being only mod- 

 erate in the case of I, but in IV amounting to a deflection of 30°. This 



