412 
PACIFIC SCIENCE, VoL XI, October, 1957 
individually on relatively large sclerites. Inter- 
coxal area with a single pair of setae between 
III, or devoid of setae; urpore present. Either 
three or two pairs of rostral setae. Palpal 
tarsus simple, cylindrical or fusiform. Larvae 
self-detaching parasites of insects, living in 
damp to very wet places, and typically with 
relatively restricted temperature tolerances. 
remarks: Not all of the variants of the 
morphological characters of the Parasitengona 
can be readily utilized in a key, but the more 
convenient ones are included here. It is in- 
teresting that the number of characters avail- 
able in the larva considerably exceeds the 
number available in the adult. Actually the 
discrepancy is not as great as would appear 
at first glance, since some adult characters are 
omitted simply because of difficulties in inter- 
preting them. 
It appears possible that thejohnstonianidae 
as defined here will require further reorganiza- 
tion as more forms become known from other 
parts of the world. At present it is quite evi- 
dent that there are two distinct groups of 
genera, the first including Centrotrombidium , 
Diplothrombium , Johnstoniana , and provision- 
ally Hirstithrombium (Johnstonianinae Thor 
1935). The second includes Lassenia new 
genus, Polydiscia Methlagl 1928, and pro- 
visionally Crossothrombium Womersley 1939 
(. LASSENIINAE new subfamily) . The princi- 
pal structural differences between the genera 
are summarized in the formula keys given 
below. 
FORMULA KEY TO GENERA OF 
JOHNSTONIANIDAE 
Based on Adults 
la. Anterior sensilla present, similar in form 
to the posterior sensilla, and at least one- 
half as long as the posterior sensilla 
(Figs. 70, 160). 
lb. Anterior sensilla present, but consider- 
ably modified, less than one-half as long 
as the posterior sensilla (Figs. 183, 232). 
lc. Anterior sensilla absent; scutum greatly 
reduced, bearing a single pair of sensilla, 
anterior to which is a single pair of nor- 
mal setae (Fig. 4). 
2a. Pregenital tubercle absent. 
2b. Pregenital tubercle present (Figs. 185, 
233). 
3a. Anal sclerites present (Figs. 18, 105). 
3b. Anus surrounded only by membranous 
cuticle containing setae, but no sclerites 
(Fig. 68). 
4a. Palpal trochanter with anterior surface 
containing a distinct oval fenestra (Fig. 
61). 
4b. Distal margin of anterior wall of tro- 
chanter deeply incised, but the fenestra 
is not completely circumscribed (Fig. 
201 ). 
4c. Anterior wall of trochanter with no trace 
of a fenestra (Fig. 69). 
5a. Eupathidia present on leg segments other 
than the tarsi. 
5b. Eupathidia confined to the tarsi. 
6a. Supracoxal setae absent from gnathosoma 
and coxae I. 
6b. Supracoxal setae present on gnathosoma 
and coxa I. 
7a. Vestigial setae absent from patella and 
tibia of all legs. 
7b. Vestigial setae present only on patella I 
and II, absent from tibiae. 
7c. Vestigial setae present on patella I and 
II, and tibia I; absent from tibia II. 
8a. Solenidia 2 of tarsus I clavate, markedly 
different in form from Si. 
8b. Solenidiai and s 2 of tarsus I differing 
primarily in size; no sharp differences in 
form. 
FORMULA KEY TO GENERA OF 
JOHNSTONIANIDAE 
Based on Larvae 
la. Scutum with four pairs of setae (two 
pairs of normal setae plus two pairs of 
sensilla) . 
lb. Scutum with two pairs of setae (one pair 
of normal setae plus one pair of sensilla) . 
