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, 0 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. 
GrEnotyPE.— M. hidalgoensis, 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. Antennae 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 35-41; 
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 
