Johnstonianidae — Newell 
405 
this is not seen however in L. scutellata so that 
the character does not seem to have generic 
significance. In the adults the palpi are always 
distinctly five-segmented. The general form 
of the palpi in the adult is basically the same 
in all genera, slightly curved but essentially 
linear in dorsal view. The same is true of the 
larvae of all of the genera except Lassenia , in 
which the palpi are geniculate, owing to the 
expansion of the posterior or posterolateral 
aspect of the femur. Associated with this ex- 
pansion of the femur, the trochanter is re- 
duced to a narrow ring. The geniculate palpi 
of Lassenia larvae are suggestive of similar 
palpi which show up at other points within 
the terrestrial Parasitengona, and in these 
cases too it is interesting to note that the 
geniculate form is lost in the transition from 
larval to nymphal stages. 
Fenestration of Trochanter of Palp 
This is a characteristic which presently ap- 
pears to be confined to the family Johnston- 
ianidae. In the larva and adult of Diplothrom- 
hium and Centrotrombidium (Figs. 33, 61, 153, 
179) there is a discrete oval window on the 
anterior (medial) aspect of the trochanter of 
the palp. This appears to be a portion of the 
cuticle which is considerably thinner and more 
transparent than the cuticle of the remainder 
of the trochanter. In Johnstoniana there is no 
trace of a fenestra. In Lassenia the situation 
is somewhat variable. In both of the known 
species the larva has a trochanter of very short 
length, probably associated with the geni- 
culate form of the palp. In this there is no 
suggestion of a fenestra. In the adult of L. 
lasseni (Fig. 201) there is a well- developed 
fenestra, but the anterior margin is not closed 
off as it is in Diplothrombium and Centrotrom- 
bidium. Thus the trochanter has the appear- 
ance of being deeply incised on the anterior 
aspect. In L. spinifera (Fig. 239) the same 
condition is found, except that here the con- 
cavity is invaded by a distinct, although feeble 
extension of the cuticle of the femur. 
The Palpal Tibia 
The form of the tibia in thejohnstonianidae 
known to date is quite constant in the larva. 
In all species there is a heavy terminal seta 
which is unidentate in Lassenia scutellata and 
Centrotrombidium distans , but bidentate in the 
other four species for which larvae have been 
adequately described. The terminal setae have 
been given a number of names by workers in 
various divisions of the Parasitengona includ- 
ing "tibial claw, tibial spur,” etc. While the 
name is not of paramount importance, it is 
well to keep in mind that this is not a claw, 
but nothing more nor less than a seta of 
unusual thickness, and it is preferable to refer 
to it as the terminal seta of the tibia. The 
term "claw” is a malapropism. In the larvae 
of all known species there are three normal 
setae behind the heavy spiniform terminal 
seta, and these may be either smooth or 
faintly pectinate. 
In the adults of all known species, the 
terminal seta of the tibia is invariably uni- 
dentate. Moreover there is always a single 
subterminal spiniform seta which may be very 
close to the terminal seta as in Lassenia and 
Diplothrombium micidium , or may be removed 
from it by a distance greater than the diam- 
eter of the alveolus of the terminal seta as in 
Johnstoniana and Diplothrombium monoense. In 
J. latiscuta there is a heavy spine near the base 
of the subterminal spiniform seta. In some of 
the Trombidiidae there is also a ctenidium com- 
posed of several stout setae arranged in a 
regular series, but this structure is not present 
in any of the known Johnstonianidae. 
Segmentation of the Legs of the Larvae 
In both species of the genus Lassenia the 
femur is completely undivided so that there 
are only five free segments beyond the coxa. 
In Johnstoniana latiscuta , there is a distinct 
synarthrodial membrane on the ventral sur- 
face of the femur, but the dorsal sclerotized 
portion of the cuticle is continuous across the 
entire length of the femur (Figs. 87, 91, 93). 
