Characters in Paratrombium — Newell 
lized in the earlier work on the Johnstonian- 
idae (Newell, 1957) has been followed, as has 
the convention for designation of the posi- 
tions of setae on the segments of the append- 
ages. The decimal system of notation has 
been extended to the scutum as well as the 
appendages. In the case of the scutum, the 
starting point (0.00) will be the most anterior 
point on the median line of the scutum. In 
Paratrombium and many other genera, the 
anterolateral lobes of the scutum actually ex- 
tend beyond this point, but since these are 
rather poorly defined in some genera or in 
particular specimens of many species, it is 
better to utilize the more readily recognizable 
point. In general this will be the most anterior 
point on the median axis of the scutum, re- 
gardless of whether or not this is precisely the 
anterior end of the entire plate. 
Attention should be called to the indiscrim- 
inate use of the term crista metopica. This 
term was applied by early authors to the very 
pronounced ridge which runs longitudinally 
over the dorsum of the propodosoma of 
many species of the Parasitengona. It is pri- 
marily a strengthening support for the dorsal 
wall of the propodosoma, and also provides 
attachment for certain of the muscles of this 
part of the body. It should be kept in mind 
that the crista metopica is only one part of a 
larger sclerite, the scutum, which is of con- 
siderably greater significance both structu- 
rally and taxonomically than the crista metop- 
ica alone. The crista metopica, because it is 
so much more conspicuous than the scutum 
(the margins of which are often so faint as to 
be detectable only in carefully dissected and 
mounted material), is often described as 
though it were an isolated structure in itself. 
In a few of the Parasitengona it does ap- 
proach this status, especially in some of the 
larger Erythraeidae in which the scutum is 
only very slightly broader than the crista. At 
some points the crista in certain genera may 
even be the only portion of the scutum to be 
found. However, such cases are extremely 
rare; and there are few species in which the 
353 
scutum does not extend at least somewhat 
beyond the limits of the crista metopica. 
The neglect of the peripheral portions of the 
scutum in descriptive accounts is a serious 
omission. It is also a mistake to extend the 
term crista metopica to apply to the scutum 
as a whole. A description of the scutum 
should be based upon dissected material, or 
if this is impossible, upon carefully com- 
pressed specimens in which all levels of the 
scutum are lying in approximately the same 
plane. 
The present study was carried out under a 
research grant (NSF-G1833) from the Na- 
tional Science Foundation to the University 
of California at Riverside. It was further aided 
by research grants from the University of 
California, which supported all of the field 
work upon which this study was based. The 
drawings were prepared by Mari Riess of the 
University of California at Riverside. In these 
figures, the scales provided are marked off in 
10 /d units except for the few marked in 100 /d 
units. The latter are drawn with a double 
base line. 
Paratrombium Bruyant 1910 
adult: Trombidiidae of medium to large 
size, and brilliant red color. Scutum with 
sensilla in middle one-third of plate, widest 
portion of scutum at anterior end; crista 
extending from posterior end of scutum 
to a group of setae near the most anterior 
point on the midline of the scutum. Eyes 
distinctly stalked, two corneae on each side. 
Dorsal hysterosomal setae all of one type, 
peripectinate, arising from small, erect, coni- 
cal papillae. Coxal rings I and II open dor- 
sally, a long slender supracoxal seta on I. 
Genital and paragenital sclerites both well 
developed and bearing numerous peripecti- 
nate setae; three pairs of genital acetabula. 
Tarsus of chelicera bearing a row of minute 
denticles along the upper margin, this row of 
denticles also continuing down over the side 
of the basal portion of the tarsus (Figs. 22, 
