Characters in Paratrombium — Newell 
possible specific nature. Correlations between 
larvae and adults in this group are much 
needed, because the two instars are often col- 
lected under quite different circumstances, 
with the adults coming from general collec- 
tions, and the larvae often being found on 
their insect hosts. Because of the great change 
in form which accompanies the transforma- 
tion from larva to nymph and nymph to adult 
in the Parasitengona, it is impossible to cor- 
relate larvae and adults with certainty by any 
means other than rearing. 
There are even more compelling reasons, 
however, for establishing correlations be- 
tween larvae and adults. In the first place, 
adults within a given genus of the Parasiten- 
gona are separated from each other by char- 
acteristics largely of a relative nature. The 
intraspecific variation in the adults of these 
mites is so great that it has not yet been ade- 
quately analyzed for any single species within 
the entire group. At the same time, inter- 
specific differences are relatively small, so that 
in examining two adult specimens within a 
given genus, which show moderate differ- 
ences, there is always the question of whether 
these differences are of a specific nature, or 
whether they fall within the range of variation 
of a single species. The primary difficulty here 
is that the chaetotactic differences which are 
of such great value in separating orthotrichous 
forms are almost totally unavailable in the 
highly neotrichous Parasitengona. With in- 
tensive study of the chaetotaxy of adults, ex- 
ceptions to this are slowly coming to light, 
but they are at the present time very few in 
number, and it appears increasingly likely 
that there are certain genera in which absolute 
chaetotactic differences will never be of great 
importance in differentiating species. While 
it is to be hoped that it will never be necessary 
to have both larvae and adults in order to pro- 
vide positive determinations of species, there 
is no assurance at this time, in the present 
inadequate state of our descriptive accounts 
of the adults of these species, that such will 
not be the case. Old species must be carefully 
351 
redescribed, and new species must be de- 
scribed in considerably greater detail and with 
far greater accuracy than they have been in 
the past if we are to progress in knowledge of 
the adults as far as we have in knowledge of 
the larvae. 
In the second place, correlations between 
larvae and adults are necessary in order to 
provide additional information upon which 
to determine relationships within the Para- 
sitengona. In very many cases, the best ge- 
neric characters are found within the larvae, 
and in any case it is always well to have the 
larval characters in addition to the adult char- 
acters in arriving at conclusions concerning 
relationship. Here again, it should be pointed 
out that even recent descriptions of larvae of 
Parasitengona are inadequate from a morpho- 
logical and systematic standpoint. All too 
often, for example, the chaetotaxy of the palpi 
is presented in a very sketchy manner, if at all, 
and the segments of the legs, despite their 
greater size, come out only slightly better. At 
the species level, detailed studies of the larvae 
of closely related species are desirable in order 
to substantiate the validity of minor differ- 
ences suspected of having specific value in 
the adults. For example, in the present case, 
there are a few very minor differences be- 
tween the adults of Paratrombium bidactylus 
and P. quadriseta. If one had only the adults 
of these two species, there would be con- 
siderable doubt whether the differences in 
eupathidial counts on the palpal tarsus, the 
slight difference in the posterior end of the 
crista metopica, the chaetotaxy of the anterior 
portion of the scutum, and the number of 
setae on genital and paragenital sclerites were 
of real specific value. It is still possible that 
studies of additional adults will show these 
characters to intergrade at least in part. Yet 
the studies of the larvae show clearly enough 
that we have two distinct species, hence any 
differences found between adults of these 
two species are of possible specific value, and 
are worth investigating in detail. 
In the present paper, the terminology uti- 
