1928] A New Species of Water Mite 93 
Thermacarus nevadensis sp. nov. 
PL III, fig. 1-9. 
The body is obovate, slightly widest in the region of the 
third pair of legs. Females measure 2.50-3.00 mm.; the males 
are slightly shorter and slimmer, the smallest, a young adi^lt, 
being but 1 . 90 mm. It is thus seen to be smaller than T. ther- 
mobius. The color of the specimens, preserved in alcohol, was 
dull olive green with some traces of red. Two individuals showed 
white irregular branching streaks on the dorsal side. The body 
is low, somewhat arched; dorsally and ventrally the integument 
is heavily chitinized to form two shields, the dorsal somewhat 
the smaller, united by a thinner layer. Heavy ridges on the 
dorsal side enclose two irregularly oval areas, one inside of the 
other (fig. 1). The double eyes of either side are outside of these 
ridges. The median sense organ is just within the larger area 
and is inconspicuous. The heavy integument shows in alco- 
holic medium a transparent, somewhat irregular layer, below 
which are low elevations irregularly scattered about on a basal 
layer; the latter shows rounded pores in groups of some ten to 
twenty enclosed in an irregularly polygonal meshwork (fig. 7). 
The conspicuous feature of the ventral side is the great 
development of the plates (figs. 2, 8, 9), the epimera closely 
resembling those of the related species. The first pair of plates, 
the largest, are fused not only ventrally but also dorsally so as 
to form a shallow cavity, reaching to the body margin or slightly 
projecting beyond it in the male, which encloses the small capi- 
tulum and the palpi. The fused epimera bear many hairs. The 
three remaining epimeral pairs are somewhat triangular, except 
that the fourth in the male is rectangular. Posterior to the 
epimera in the new species is another plate, a large median one, 
heavily chitinized and bearing the so-called anal spot, differing 
in size and shape in the two sexes and in contour in individuals 
of differing ages, and completing the closure of the genital areas. 
The genital area in the male (fig. 2) is nearly circular, past 
the center of the body and enclosed by the fourth epimera and 
the medial posterior plate. Its valves are heavily chitinized 
