
AUSTRALIAN ACARINA 
Tur Genera BRACHYCHTHONIUS Bert. ann COSMOCHTHONIUS 
Bert. (HYPOCHTHONIDAE-ORIBATOIDEA) 
By H. WOMERSLEY, F.R.E.S., A.L.S., Enromotocisr, Sourn AusrrALiAN Museum. 
Tue species of the genera dealt with in this paper are very small, colourless to yel- 
low mites found inhabiting moss. Owing to their small size, under 0-30 mm, in 
length, special methods of collecting are required, generally by putting the moss 
through the special funnel invented by Berlese. Hitherto the genera have not 
been recorded from Australia, but recently in samples of moss brought back from 
Normanville (September, 1943) and Quorn, South Australia (November, 1943), 
1 have found representatives of five species of which three can probably be referred 
to European forms, the others being new. The specific characters of these small 
mites, of which about a dozen species are described, are found in the presence or 
absence of dorsal seulpturing, and when present its nature, and more particularly 
in the structure and comparative length of the sensillary or pseudostigmal setae, 
and of the normal dorsal setae. Unfortunately workers on this group have been 
content. with comparing the lengths of the dorsal setae of the various species in 
general terms and not in actual dimensions. With such mites as these inhabiting 
moss, and of which both the mosses and the mites are extremely archaic and cos- 
mopolitan, or widely spread by commerce, or both, it. is extremely difficult to 
refer specimens to descriptions from other countries without access to authentic 
material, unless actual setal lengths are given. 
Consequently while some of the species here recorded from South Australia 
are only referred to European forms, the setal lengths of the latter are required 
for a final decision. 
Genus BracuycutTHontus Berlese. 1910. 
Acari Nuovi. Manip. VI. Redia 6, p. 219, 1910. Genotype B. brevis (Mich., 1888). 
Belonging to the subfamily Hypochthonidae of the Oribatoidea, differentiated 
by the mandibles being more or less covered by the rostrum ; a distinet. separation 
of propodosoma and hysterosoma ; the anal and genital openings oceupying most, of 
the area behind coxae IV, broadly contiguous, the anal opening usually narrowing 
posteriorly ; and the hysterosoma with one or more transverse sutures. The genus 
is distinguished by two sutures forming 3 plates on the hysterosoma, of which 
the anterior suture is entire, and by having none or only a single lateral plate. 
BRACHYCHTHONIUS ef, PERPUSILLUS Berl. 1910. 
Acari Nuovi, Manip. VI. Redia 6, 220, fig. 41, 1910; nec, Jacot, 1936. 
Fig. 1 A-C. 
Light coloured species, 234. long by 117p wide. Sensillary setae 32, long 
with fusiform head of about half its length furnished with several longitudinal 
rows of 5 denticles in each; the basal cup is 12 long with the mouth 10p in 
diameter. Dorsal setae acicular-foliaceous with prominent rib, similar on both 
propodosoma and hysterosoma, rostral and interlamellar setae 16p long, re- 
mainder 13. 
