178 Psyche [December 
gaster. Like most other Pselaphids of myrmecophilous habits, 
few are found in a single ant colony, but they are generally common, 
there being one or two in almost every nest of the host ant in the 
localities where they occur. 
Family HistEripm. , 
Hetzrius helene sp. nov. 
Length 2mm. Color reddish-brown, in some specimens the side margins of the 
head, the margin of mandible and apex of femur piceous; shining. Form robust, 
about two-thirds as broad as long. Head above sparsely, coarsely punctate, less 
so between the eyes and beneath; clypeus about twice as broad as long, finely 
punctate; front with short yellow hairs. Thorax transverse, its breadth nearly 
twice the length; broadest at base; front border concave, narrowly margined; sides 
straight to the constriction, which is located about five-eighths the distance from the 
anterior angle to base; median portion of disc finely, regularly punctate, with 
sparse yellow hairs; marginal portion in front of constriction very finely rugose 
longitudinally and less shining than the remainder of thorax; the anterior border 
feebly rounded, posterior portion slightly elevated; margin of sides with a rather 
dense brush of long stiff yellow hairs. Elytra at base distinctly broader than 
thorax, the width of both together about equal to length; abundantly pilose; apical 
margin punctate; marginal and humeral striz entire; third and fourth striz extend- 
ing for five-sixths the length of elytra, carinated for entire length. Propygidium 
and pygidium finely rugulose, the former with sparse long hairs. Posternum 
narrowly margined for half its length; transversely impressed at half the distance 
from end of margination to anterior border; distinctly excised at anterior border; 
margined portion shining, smooth behind and finely punctate in front. Anterior 
tibize nearly a third as broad as long, the front margin posterior to the angle straight, 
with about eleven elongate denticles. Middle and posterior tibize one-third as 
broad as long, the outer edge rounded. 
There is considerable variation in the shade of color and a little in size. The 
hairs are rather long, curved, and moderately abundant. In some specimens they 
are almost entirely absent, probably having been scraped off by the ants. 
Described from a number of specimens taken in nests of Formica 
subcyanea Wheeler and F. microgyna subsp. rasilis var. nahua 
Wheeler. The former ant is the favorite host, as nearly every 
nest in some localities contained the beetles, while they were 
found in only one nest of the latter species out of dozens examined. 
This species, the first known from Mexico, is more closely re- 
lated to some undescribed forms from our southwestern states 
than to any of the described species. It is more pilose than any 
of the species which I have seen, except californicus and an unde- 
scribed species (hirsutus mss.) from Arizona. 
