540 bulletin: museum of comparative zoology. 



produced, those of ninth weakly so. Fourteenth tergite of normal 

 form. 



Coxal pores small, circular; uniseriate. 



Claw of female gonopods strictly entire as always. Basal spines 

 2 + 2, conically acuminate. Inner edge of first article well chitinized ; 

 Article furrowed across base. 



Posterior legs of male without special lobes or modifications. 



Posterior coxae dorsally and laterally armed in type. Ventral 

 spines of anal legs 0, 1, 3, 2, or 0, 1, 3, 2, 1, rarely 0, 1, 3, 3, 1 ; dorsal, 

 1, 0, 3, 1, 0; claws 2, the accessory large and distinct. Ventral spines 

 of penult legs 0, 1, 3, 3, 1; dorsal, 1, 0, 3, 2, 1, more rarely only 

 1, 0, 3, 1, 1. Dorsal and ventral spines of first legs 0, 0, 1, 2, 1. Legs 

 from second to thirteenth with 2 dorsal tibial spines. 



Length up to 18 mm. 



Genotype. — M. hidalgocnsis, sp. nov. 



This genus is close to Arenobius in its restricted sense with which 

 it agrees in the unusual character of the prosternum. It is most 

 readily distinguished by the large number of antennal articles, the 

 number in Arenobius being fixed at 20. It also differs in wholly lack- 

 ing the special lobes characterizing the anal and penult legs of males 

 in Arenobius. 



Mexicobius hidalgoensis, sp. nov. 



Dorsum clear shining brown to dusky brown, the first plate typically 

 somewhat darker than the others. Head brown of a dilute ferruginous 

 tinge, dusky caudad of the suture. xA.ntennae dusky or blackish 

 brown, rufous at tips and also paler proximally. Prosternum brown, 

 the prehensors similar but rufous distally. Venter light brown, the 

 legs similar to venter, brighter distad; the caudal pairs not clearly 

 differing in color from the others. 



Body moderately attenuated cephalad. The widths of head and of 

 first, third, eighth, tenth, and twelfth plates to each other as 72:70: 

 74:83:85:80. 



Head widest at level of marginal breaks; widely rounded anteriorly; 

 caudal margin straight. Marginal breaks small but distinct. Weakly 

 punctate. The usual median sulcus in front of the suture. Equal in 

 length and breadth or very nearly so. 



Antennae very short; strongly narrowed distad. Articles 35^1; 

 the first two of moderate length, the third shorter and the remaining 

 ones very short and closely crowded ; the ultimate article shorter than 

 the two preceding ones together. 



Ocelli 14 to 26 in four or, less commonly, (pseudomaturus) in three 



