Johnstonianidae — - Newell 
403 
setae. In fact, in Diplothrombium micidium the 
setae on the paragenital sclerites actually out- 
number those on the genital sclerites proper. 
In the other terrestrial Parasitengona, the 
paragenital sclerites bear markedly fewer setae 
than the genital sclerites, if they bear any at 
all. There are invariably three pairs of genital 
acetabula in both the male and female. The 
penis of the male is relatively very small. A 
unique variant in the genital area is found in 
Lassenia in which there is a well developed 
pregenital tubercle. In Lassenia lasseni this 
makes its first appearance in the protonymph 
and increases in size in the deutonymph and 
adult. In L. lasseni it is a simple hemispherical 
tubercle, while in L. spinifera it is an elongate 
peduncle. In both cases it is heavily sclero- 
tized and pigmented in the mature adult. Not 
even a rudiment of this pregenital tubercle 
has been found in the larvae, nymphs or adults 
of any of the other genera. 
Anal Area 
In all genera but Lassenia and Polydiscia the 
anal anlage of the larva is a simple slit with 
no associated setae. In both Lassenia lasseni 
and L. scutellata the slit is guarded by a pair 
of anal sclerites bearing two pairs of simple, 
smooth setae. The anal sclerites of the adults 
of all but Johnstoniana are distinctively cres- 
centic in form, bearing in most cases a single 
row of smooth, simple setae (Figs. 18, 105, 
240). In Lassenia spinifera there are two rows 
of setae on the anal sclerites, whereas in at 
least one male of Lassenia lasseni , the two anal 
sclerites had only 0 and 1 setae respectively. 
Perhaps the most significant variant is found 
in Johnstoniana latiscuta in which there are no 
anal sclerites at all (Fig. 68) . There is a poorly 
defined anal area bearing a number of setae 
and differing from the surrounding cuticle 
only in the absence of striae. 
Rostral Setae 
The situation with regard to these setae 
cannot be finally resolved until further studies 
are made in other families. However, if we 
take Lassenia lasseni as a starting point, we find 
in the larva of that species three pairs of setae 
on the gnathosoma, all of these on the ros- 
trum (Fig. 229). These will be called the 
proto-, deuto-, and tritorostral setae, and the 
presence of these three pairs is a condition 
characteristic of the larvae of many genera of 
the terrestrial Parasitengona. The protorostral 
setae are generally located dorsally or dorso- 
laterally on the tip of the rostrum, not only 
in this species but in the terrestrial Parasiten- 
gona in general. (These are the so-called 
"galea! setae" of specialists in the Trombi- 
culidae. The writer prefers the term "proto- 
rostral setae" because it is simpler to give 
these three topographically related setae paral- 
lel names than to coin separate ones for each.) 
In L. lasseni , the deutorostral setae are under 
the margin of the velum in both the larva 
and the adult (Figs. 188, 229), while the tri- 
torostral setae lie directly behind them. In 
Centrotrombidium distans , Diplothrombium and 
Johnstoniana there are only two pairs of setae 
in the larva (Figs. 45, 170, and 88). The distal 
pair of setae obviously are the protorostrals 
while the basal pair are either deutorostrals 
or tritorostrals. In larvae of Centrotrombidium 
distans (Fig. 45) a pair of very minute struc- 
tures of uncertain nature is found along the 
margin of the velum in approximately the 
position occupied by the deutorostral setae 
of Lassenia lasseni. Apparently homologous 
structures are found in the adult as well (Figs. 
2, 17). These may represent highly modified 
setae, or they may simply be points of inser- 
tion of muscles associated with the velum. 
Homologous structures have been found also 
in adults of Diplothrombium monoense , but 
neither in the adults nor the larvae of John- 
stoniana latiscuta . From their position alone 
these would appear to be homologous with 
the deutorostral setae of Lassenia so that the 
series Lassenia— ( Centrotrombidium , Diplothrom- 
bium) — Johnstoniana represents a progressive 
diminution in the size and importance of the 
deutorostral setae. This conclusion should be 
verified with studies in related genera and 
