Occasional Papers of the Museum of Zoology 83 



margin often vaguely crenate in correspondence with all or 

 most of these border areas. The fourth and immediately fol- 

 lowing keels narrowing and rounded distad; those of more 

 posterior segments more quadrate. (PL 30, Fig. 212.) Cau- 

 dal margin of keels of last few segments oblique, the caudal 

 angle becoming acute, those of the eighteenth more strongly 

 bent back, while those of the nineteenth nearly meet in the 

 middle line and widely overlap the last segment in the usual 

 manner. Across each ordinary metatergite two rows of long 

 setae, typically six setae in each series between the keels. 



Cauda of anal segment narrow, distally rounded, not reach- 

 ing caudal edge of keels of nineteenth segment. Anal scale 

 broad, triangular, the caudal angle extending beyond the 

 tubercles. 



Length, about 16 mm. ; width, 2.5 mm. 



Colombia : San Lorenzo. July 3, 1913 ; F. M. Gaige. One 

 female imder log at 4.500 feet. Holotype, ]\L C. Z., 5.188. 



Easily distinguished from A. z'crrucosus (Brolemann), the 

 genotype, by dilTerences in the coUum. In the latter species 

 the collum is crossed by two series of setae in which those of 

 the posterior series are larger. In thrixophor, on the contrary, 

 there is an anterior series of long setae, while the remaining 

 part of the plate bears shorter setae. 



