NORTH AMERICAN SPECIES OF THE GENUS AT AX 213 



the outer side are two toward the extensor margin, the distance between 

 them somewhat less than one-third the length of the segment. Segment 

 3 is much shorter than 2 and not so broad, yet broader than long. Its 

 flexor side is half the length of the extensor, each of them with a slight 

 convexity, and there is a small straight spine on the outer side, while 4 is 

 longer and narrower, concave on its flexor surface, moderately convex on 

 the opposite side. The former bears distally a pair of not very prominent 

 papillae and a short spur at the distal margin. Segment 5 tapers at first 

 rapidly, then more gradually to a blunt, rounded tip, produced slightly 

 toward the flexor side and bearing at the distal end four short claw-like 

 projections arranged in quadrille, while immediately proximad of them 

 are two very short spines. 



Epimera covering about the same proportion of the ventral surface as 

 do those of A. figuralis, but II and III and those of opposite sides are 

 separated only by very narrow spaces, narrower in the male than in the 

 female. Outline of the fused I and II approximately triangular, the apex 

 of the triangles of the two sides nearly meeting in the median line. The 

 anterior margin of this triangular plate is slightly excavated and the 

 posterior forms a double curve, being convex for the inner two-thirds of 

 its length and beyond that concave. I is long and narrow, broadly ex- 

 panded at its outer end, where it is moderately excavated to receive the 

 first pair of legs, while II is broadly triangular with the anterior external 

 angle truncate. The plate formed by the fused III and IV has a slightly 

 concave anterior margin, a nearly straight inner margin, and a posterior 

 margin slightly convex, all the angles being rounded. The epimera of 

 the opposite sides approach each other most closely in front. A trans- 

 verse suture two-fifths of the distance from the anterior to the posterior 

 margin indicates the line of junction of the two epimera. 



The legs are shorter than in the related species and relatively longer 

 in the male than in the female. In the former I is slightly longer than 

 the body, II and III about equal and each a little less than one-third 

 longer, IV about two-thirds longer. I of the female is almost four-fifths 

 of the body length, II and III somewhat exceed it and IV is greater by 

 a little more than one-third. Of the individual segments 1 is the shortest 

 and the others gradually increase in length to 5, but 6 is again shorter. I 

 is slightly heavier than the rest, though as a whole the legs are decidedly 

 weak and the distal segments especially slender. There are no movable 

 spines on I set into projecting sockets as in A. crassipes and A. figuralis, 

 their number is somewhat less, and individually they are shorter and 

 more slender and taper to a sharp point. The claws are characteristic. 

 Those on I are expanded dorso-ventrally and flattened laterally, forming 

 a broad plate of which the dorsal margin is strongly arched, the flexor 

 margin deeply pectinate, the pectinations, about sixteen in number, reach- 

 ing nearly three-fourths the distance to the opposite margin, and with a 

 slight curvature toward the base of the claw. The claws of the remaining 

 legs are slender, strongly curved at the base, more moderately beyond, 

 and again more strongly toward the sharply-pointed tip. On the whole 

 the claw of II has the more pronounced curvature and is shortest, IV the 



