Johnstonianidae — Newell 
441 
ther evidence of the narrow temperature toler- 
ance of D. monoense was obtained through an 
unfortunate mishap. A number of adults be- 
ing brought back to Riverside for rearing 
studies were killed during the eight-hour 
transit of the Mojave Desert, despite precau- 
tions taken to insulate them from the heat. 
The same was true of the living specimens of 
Lassenia lasseni— none survived the trip across 
the desert. At the same time a species of 
Microtrombidium collected at an elevation of 
8,000 feet on the slopes of Mt. Lassen did 
survive, laid eggs, and these eggs eventually 
hatched. A species of Erythraeidae also sur- 
vived the exposure to high temperature which 
was lethal to the two species of Johnstonia- 
nidae. The rather low heat tolerance of these 
species undoubtedly is important in deter- 
mining their distribution, both geographically 
and locally. 
The correlation between larva and adult 
was established on the basis of their co- 
existence at the type locality. More than 90 
adults or nymphs and 50 larvae have been 
collected there, and there is apparently only 
one species involved. 
Diplothrombium micidium new species 
female: Body (Fig. 152) 936 /* to tip of 
scutal spine, 546 fi wide, length/width 1.48 
(one ovigerous female). Scutum (Fig. 160) 
produced into a stout conical spine anteriorly. 
Crista metopica well developed, extending 
from posterior end of scutum to base of spine. 
Two pairs of sensilla present, the posterior 
pair borne on the widest portion of the scu- 
tum; sensilla completely smooth. Just in front 
of the posterior sensilla are two pairs of 
smooth setae, and just lateral to the sensilla 
a third pair of setae which lie either in the 
very margin of the scutum or possibly in 
some cases just outside. The rather broad 
plate found behind the posterior area sensil- 
ligera in Diplothrombium monoense is also found 
in this species but it is small and easily over- 
looked at low magnification. Ocular plates 
very small, bearing two protruding corneae; 
devoid of setae. Dorsal propodosomal cuticle 
containing about 20 setae on each side be- 
tween the ocular plate and the scutum; each 
of these setae is borne on a small sclerite. 
Dorsal hysterosomal setae (Fig. 167) also 
borne on individual sclerites, the shaft sharply 
deflexed at the origin of the seta from the 
alveolus. Membranous cuticle of dorsum 
smooth, subcuticular reticulum present but 
not very prominent. Coxae I and II (Fig. 154) 
each with about 30 or 31 smooth simple 
setae, pars medialis coxae with three to four 
setae each borne in an oval area within the 
pars. Outside of these oval areas the pars 
medialis is distinctly reticular in appearance. 
Supracoxal setae absent on I. Intercoxal area 
with about 60 setae borne on individual scler- 
ites in the specimen studied (not all shown 
in the figure), these setae smooth and simple. 
Two to three narrow refractile chitinous rods 
in the membranous cuticle behind coxa II; 
a band of membranous cuticle behind coxa 
II devoid of setae. Coxae III and IV (Fig. 
165) each with about 25 to 30 setae. Genital 
sclerites (Fig. 164) with 10 and 12 setae each 
in a single row; paragenital sclerites with 19 
and 22 setae each in a single to double row. 
Three pairs of genital acetabula present. Anal 
sclerites narrow, crescentic, bearing 9 smooth 
setae each in the specimen studied (Fig. 158). 
Ventral setae of hysterosoma all borne on 
individual sclerites as on dorsum. 
Rostrum (Fig. 154) with telorostral and 
deutorostral setae well developed; remainder 
of rostrum and base of gnathosoma with 30 
setae on each side of the mid-line; mid-ven- 
tral portion of gnathosoma devoid of setae. 
Velum small, anteriorly directed, with nu- 
merous converging filaments. Base of cheli- 
cera (Fig. 166) compact, densely and minutely 
punctate; dorsal membrane blunt, tarsus 
stout, curved, dorsal margin appearing smooth 
at low magnifications but with a very large 
number of minute teeth at magnifications 
above 250 x. Palpi (Fig. 153) with trochanter 
fenestrated on anterior surface, femur with 20 
