464 
PACIFIC SCIENCE, VoL XI, October, 1957 
The major points of similarity to Lassenia 
are the presence of two pairs of sensilla on the 
scutum (not a single pair as assumed by 
various authors), the large setigerous sclerites 
covering the dorsum, the 2-1-2 setal formula 
of the coxae, the presence of distinct seti- 
gerous anal sclerites, and the tridactyl tarsi of 
the larva. There are however, certain differ- 
ences such as the apparently rectangular form 
of the base of the gnathosoma, the simple 
form of the palpi, the absence of a clawlike 
seta on the tibia of the palp and the sub- 
division of the femora of the legs, (provided 
these were all accurately represented in the 
original descriptions, which is improbable). 
The fact that the anterior pair of setae of the 
scutum were not considered sensilla undoubt- 
edly stems from the weak development of the 
alveoli of these setae. Precisely the same situa- 
tion is found in Lassenia scutellata (Fig. 249), 
although close study of these setae at high 
magnification shows that they do have some- 
what more elaborately developed alveoli than 
do the other setae of the scutum. The anterior 
setae of Lassenia lasseni are even less sensillar 
in form, although there is no doubt whatever 
that these are the true homologs of the an- 
terior sensilla of such forms as Diplothrombium. 
Thor and Willmann (1947, p. 343) stated 
that this was "wahrscheinlich ein Trombidio- 
seerreger.” Methlagl (p. 247) stated that 
Polydiscia squamata was responsible for trom- 
bidiasis in the vicinity of Vienna, although he 
earlier (p. 225) indicated that he had never 
found it on any host. Apparently the correla- 
tion between trombidiasis and Polydiscia was 
based solely on the seasonal abundance and 
general appearance of the latter. But this type 
of correlation can lead to absurd results as 
Methlagl himself (p. 247) so clearly showed 
when, on similar evidence, he supposed 
Hauptmannia longicollis Oudemans to be the 
larva of Anystis vitis (Schrank) . For the present 
we can only conclude that Polydiscia squamata 
has not been shown to play any role in trom- 
bidiasis of man. On the contrary, its similarity 
to Lassenia scutellata (and hence to L. lasseni ) 
is good presumptive evidence that larvae of 
P. squamata are parasites of insects and not 
of vertebrates. 
Crossothrombium Womersley 1939 
This South Australian genus has been 
generally overlooked in recent catalogs (Thor 
and Willmann, 1947; Radford, 1950; Baker 
and Wharton, 1952). As Womersley pointed 
out, it is allied to Johnstoniana , and therefore 
belongs in the Johnstonianidae. However, 
contrary to Womersley’s diagnosis, the holo- 
type, Crossothrombium parkhousei Womersley 
1939, appears to have two pairs of sensilla. 
The anterior pair, as in the case of Lassenia , 
is appreciably different from the posterior 
pair, but nevertheless they must be regarded 
as the homologs of the anterior sensilla. 
Womersley indicated that the eyes are absent 
which would be a significant point of differ- 
ence between this genus and all of the others 
of Johnstonianidae. He also indicated that 
the dorsal setae arise from large "pits or 
circles,” which are evidently the setigerous 
sclerites so typical of the Johnstonianidae. 
The tarsus of the palp was described as being 
"without terminal spines.” If "spines” in this 
case means eupathidia, this would be unique 
in the family. This, too, requires verification. 
The description of both the genus and the 
species are too fragmentary to permit com- 
parison with other genera of the family. One 
of the characters that can be seen in the fig- 
ures is that there are several setigerous scler- 
ites lying lateral to the scutum. 
The species was described from a single 
specimen collected in South Australia, and 
was subsequently recorded from Victoria, 
Australia (Womersley 1942, p. 172). 
Myrmicotrombium Womersley 1934 
The original diagnosis of this genus was as 
follows: "Crista short, with two sensillary areas 
at anterior and posterior end. One eye on each 
side, in front of the anterior end of crista. 
Body as in Microtrombidium . Tarsi at end 
truncate, with one or two small, raised prom- 
