154 
J. R. AUDY 
Remarks . — Both the oudemansi- and the lacunosa-giowp are immediately recognisable by 
the general appearance of the scutum. There is a most convincing similarity which is difficult 
to convey by illustrations or words. There is wealth of material from Malaysia and Australasia 
and it is premature to discuss this group until further studies have been made. We need only 
note that it is exceptional for members of the oudemansi - group to have toothed chelicers, and 
that femora II and III are imperfectly divided in several members of the lacunosa- group. 
Therefore we either have an extraordinary close convergence in two different groups, or they 
are but one, and the lacunosa - group should be included in Walchiella , which may then be 
restored to generic rank. 
World species (Asia & Pacific ). — lacunosa NA , ?lawrencei ( =guntheri), nadchatrami N , phascogale 
sarawakensis, smithi , zvongabelensis , 4 n. spp. in MS. 
? New subgenus : indica-group 
Representative Species. — Schongastia indica Hirst, 1915:187, Bull. ent. Res., 6, 183-190. Common 
and widespread, especially on rodents (including house-rats) in Asiatic-Pacific area. 
Provisional Diagnosis . — Species of Euschongastia whose larvae have small subquadrate scuta, usually 
lightly chitinised, with AW 20-50(0. and AP 20-30(0 ( Pexcept in rattus , AP 42) ; AM in advance of ALs with 
the shoulders of the scutum rounded in front of ALs; AM longer than ALs; posterior scutal margin 
sinuous or slightly convex ; sensillary bases about centrally placed, sensillae clavate with a basal stem, not 
globose; eyes present or absent; legs usually short with relatively thick, stumpy segments, frequently 
with one or more nude setae on tarsus III, body and leg setae usually delicately barbed or ciliated, not 
stout or plumose. Nymphs & Adults (described for indica , audyi ) apparently not distinctive, of general 
Euschongastia facies with ASL: SB ratio almost 2; sensillae hirsute, slightly thickened in audyi. N.B.: 
debilis , labuanensis, are exceptions noted below. 
Remarks. — Eusch. indica is the dominant species infesting domestic rats in villages and 
towns from India to Malaysia and the Philippines ; its range extends to Guam and New Guinea. 
In Malaya it is also a dominant species infesting tree-nesting rats in plantations and the forest- 
edge, but within the forest it is replaced by audyi , which was first collected in South Burma in 
1945. E. audyi is red ( indica being white) and it is a dominant chigger on arboreal mammals 
in the forests in Malaya and Borneo. Gispen (1950) has recovered pathogenic rickettsiae 
from indica in Java, and Traub et al. (1950) have recovered R. tsutsugamushi from a species from 
Malayan squirrels recorded as indica but subsequently described as audyi (see footnote, Traub 
and Audy, 1953, this Study p. 77 ). This is clearly an important group. A good deal of 
nymphal and new larval material is at hand and its study may allow the limits of this group to be 
defined. It is necessary to clarify the relationships between the indica - group as here defined 
and (a) the uncertain genera Ascoschongastia and Pseudo schongastia and ( b ) such species as 
debilis and labuanensis , and (c) the genus Doloisia sensu lato. It is worth noting the 
extraordinarily close resemblance between Trombicula munda and Euschongastia indica — they 
are very easily confused if the sensillae are missing : there has been a very close convergence of 
characters in the larvae of two genera. E. labuanensis is very close indeed to E. roluis Traub 
and Audy, 1953 (this Study p. 79 ), but (sensillae excluded) it differs from it no less than 
T. munda differs from E. indica. It is clearly necessary to be cautious and the present writer 
would prefer to leave debilis and labuanensis sub judice. In both, the AM seta is in line with or 
slightly behind the line of the ALs and the anterior scutal shoulder is lacking; in labuanensis 
the concave posterior margin suggests a possible relationship with such species as E. andrei. 
There may be confusing intermediate forms linking the indica - group to Doloisia and there 
appear sound reasons for regarding Ascoschongastia at least as a sister group. 
The exceptional depth (AP 42^) of the scutum of E. rattus appears to be partly due to a 
fracture in the very poorly chitinised scutum, visible under the phase-contrast microscope in a 
paratype kindly lent to the writer by Womersley. 
Old World species (Asia & Pacific ). — audyi N (A unpub.), daria T. & A. ( N unpub.), indica NA 
( = cockingsi N ), indicella T. & A., lorius , ocellifera T. & A., roluis T. & A. (N unpub.), rattus , soekaboemiensis , 
2 n. spp. unpub. (species with authors T. & A. are new species, this Study pp. 77-88). 
STUD. INST. MED. RES. 
