Johnstonianidae — Newell 
411 
Distribution of Coxal, Supracoxal and Vestigial Setae (Larvae) 
No. Coxal 
Setae 
J. latiscuta 2-1-1 
D. monoense 2-1-1 
D. cascadense 2-1-1 
C. distans 2-1-1 
L. lasseni 2-2-3 
L. scute llat a. . . 2-1-2 
setae in the larvae of the known Johnston- 
ianidae is summarized in the table given 
above. Although this table is based on the 
larvae, the figures would be identical for the 
adults except for the number of coxal setae. 
The Specialized Setae of the Palpal Tarsus of the 
Larva 
One constant feature in the chaetotaxy of 
the palpal tarsus of the larva is the presence 
of a single solenidion on the posterior aspect 
of the basal one-third of the segment. The 
tarsal eupathidia exhibit one interesting vari- 
ant. In both species of Lassenia these are of 
typical eupathidiform structure, tubular 
throughout, and relatively thin-walled. More- 
over, the terminal eupathid is always at the 
very end of the segment (Fig. 253). In the 
other three genera, the end of the tarsus 
always extends beyond the insertion of the 
most distal seta. Moreover, none of the tarsal 
setae in larvae of these three genera are 
typically eupathidiform, although it may be 
presumed that some of the terminal ones are 
homologous with the typical eupathidia of 
Lassenia. These subterminal setae are strongly 
hemipectinate, and in Centrotrombidium dis- 
tans , the one nearest the end of the segment 
is also flattened and expanded (Figs. 28, 29, 
92, 176). 
The Specialized Setae of the Palpal Tarsus of the 
Adult 
While in the larva the solenidion on the 
posterior surface of the palpal tarsus is always 
in the basal one-half or one-third of the seg- 
ment, in the adult there is a strong tendency 
Supracoxal Setae 
Vestigial Setae 
Palpi 
I 
I 
II 
pa ti 
pa 
ti 
0 
0 
1 0 
1 
0 
0 
0 
0 0 
0 
0 
0 
0 
0 0 
0 
0 
0 
0 
0 0 
0 
0 
1 
1 
1 1 
1 
0 
1 
1 
1 1 
1 
0 
for the solenidion to be displaced toward the 
distal end. In Centrotrombidium it is found at 
roughly 0.3 p, in Diplothrombium at approxi- 
mately 0.5 p, and in Johnstoniana and Lassenia 
at approximately 0.8 to 0.9 p. Paralleling the 
displacement of the solenidion is an increase 
in number of eupathidia. Thus, in Centrotrom- 
bidium there are only 2 terminal eupathidia, 
but in Diplothrombium there are 3 to 5, in 
Johnstoniana about 6, and in Lassenia from 6 
to 15 depending upon the species and the 
individual. These trends are not entirely asso- 
ciated with size for although Diplothrombium 
micidium is smaller than D. monoense , the num- 
ber of eupathidia on the tarsus of the palp is 
greater. Also the tarsus of the palp of John- 
stoniana latiscuta is larger than that of Lassenia 
spinifera , yet there are only about half as many 
eupathidia. 
DESCRIPTIONS AND KEYS 
JOHNSTONIANIDAE new family 
diagnosis: Adults with genital and para- 
genital sclerites about equally developed, and 
with three pairs of genital acetabula. Scutum 
with two pairs of typical sensilla, or with 
anterior pair greatly modified to absent. Scu- 
tum frequently with an anterior spine. Hys- 
terosomal setae typically smooth, borne on 
individual sclerites. Chelicerae as in Trombi- 
diidae, with base, movable tarsus, and a 
delicate dorsal membrane. Palpal tibia with- 
out ctenidium, with only the one terminal 
and one subterminal spiniform setae. Anterior 
wall of palpal trochanter often fenestrated. 
Larvae also with one to two pairs of sen- 
silla on the scutum. Dorsum with setae borne 
