ACARINA FROM ‘THE JUAN FERNANDEZ ISLANDS 565 
Plateremzeus BERL. 
In 1888 BERLESE briefly described and delineated from Matto Grosso in 
Brazil two new Oribatei, viz. “vema@us carinulatus and Damaeus ornatissimus. 
In 1908 he established the new genus Plateremeus, unfortunately without giv- 
ing any diagnosis but confining himself to indicating 1). ovnatisstmus as type 
of the new genus and leaving it to later investigators to find out for them- 
selves the features of this genus. To this genus he added first Lvreme@us com- 
planatus BERL. described already in 1901 from Chile, and later on PZ. rotun- 
datus from Java. The last species is so well delineated, that it is at least pos- 
sible to get a fairly good idea of what features constitute the chief character- 
istics of the genus. 
Common to all four species is the flattened or slightly concave dorsal 
side and the broadly rounded hysterosoma, the length of which is only about 
I.2 times the width. 
BERLESE does not give us any data about the size and shape of the 
genital and anal plates but his description of P. ornatsstmus furnishes us with 
some very interesting details about the legs (I. c. p. 218): »Pedes omnes ut in 
Dameus Dugesti (Europe) fabricati, sed paullo crassiores, articulis omnibus 
laciniatis, laciniis terreis ut in pedibus eolzodes Doderleinii (Europe) dispositis». 
As a matter of fact Plateremeus resembles both Gymnodameus, to which 
D. Dugesi belongs, and Platyliodes, to which NV. Doderlemi belongs. 
Fortunately the fund of a new species of this genus in Juan Fernandez 
enables me to supply the generic diagnosis of Plalerema@us so badly needed. 
There are two specimens in the collection and they differ in one important 
respect: one is quite naked, whereas the other carries four dorsal shields, which 
are very thin but undoubtly represent the dorsal shields of the 4 developmental 
stages, exactly as in Weoliodes and Platyliodes. It is evident that this cover 
very easily falls off either during the life time of the animal or after its death, 
in the last instance due to the action of the preserving fluids. 
It is in this connection worth mentioning that even PAOLI in his excel- 
lent paper on Dameosoma and allied genera (1908) failed to find these exuvie 
in Licneremeus although he carefully investigated four species. It was BER- 
LESE who subsequently (1910, p. 229, fig. 71 pl. 21) discovered them both in 
L. cesareus BERL. and'in L. latiflabellatus. 
The fund of these exuvize in the new species from Juan Fernandez en- 
ables us to draw the conclusion that they are present also in the other species 
of Plateremeus, although they easily fall off, and to add this characteristic feature 
to the generic diagnosis of Plateremaus, that the dorsal side of the hysterosoma 
is covered by one larval and three nymphal skins. 
Another feature which is obviously of generic value is the peculiar cover 
of some secretion which completely envelops the whole animal, including even 
the legs and the pseudostigmatic organs. This cover adheres so closely to 
the cuticle, that it looks as if it were the cuticle itself. It has a reticulated 
surface and is of a spongy texture (fig. 24) but mixed with numerous small 
spinules, which seem to be cuticular and indeed are so deceptive that I mis- 
