ACARINA FROM THE JUAN FERNANDEZ ISLANDS 565 



Platereiiiaeus Berl. 



In 1888 Berlese briefly described and delineated from Matto Grosso in 

 Brazil two new Oribatei, viz. Eremcetis carinulaUis and Dani<£us ornatissimus. 

 In 1908 he established the new genus Plateremceiis, unfortunately without giv- 

 ing any diagnosis but confining himself to indicating D. ornatissimus 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 Eremceus com- 

 planaius Berl. described already in igoi from Chile, and later on PL rottin- 

 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 

 1.2 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. ornatissimus furnishes us with 

 some very interesting details about the legs (1. c. p. 218): »Pedes omnes ut in 

 Damceus Dugesii (Europae) fabricati, sed pauUo crassiores, articulis omnibus 

 laciniatis, laciniis terreis ut in pedibus Neoliodes Doderleinii (Europae) dispositis». 



As a matter of fact PlateremcEus resembles both Gymnodamcsus, to which 

 D. Dugesii belongs, and Platyliodes, to which N. Doderleinii belongs. 



Fortunately the fund of a new species of this genus in Juan Fernandez 

 enables me to supply the generic diagnosis of Plateremceus 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 Neoliodes 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 exuviae 

 in Licneremceus although he carefully investigated four species. It was Ber- 

 lese who subsequently (1910, p. 229, fig. 71 pi. 21) discovered them both in 

 L. ccusareus Berl. and in L. latijlabellatus. 



The fund of these exuviae in the new species from Juan Fernandez en- 

 ables us to draw the conclusion that they are present also in the other species 

 of Plateremceus, although they easily fall off, and to add this characteristic feature 

 to the generic diagnosis of PlateremcEus, 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- 



