PK. JOHNSTON ON THE ACA&IDES OF BEBWICKSHIBE. 311 



downwards, and those of the tarsus exceed the claw even 

 when this is fully stretched out. There is no second claw, 

 but a short spine, often scarcely to be seen, on the inner side 

 of the joint at its base. The colour of the integument of the 

 mite, when bruised and compressed, is pitch-brown. 



The walk of the Acarus geniculatus is slow and measured ; 

 and when it falls on the back, it recovers the right position 

 with great difficulty. It rests with all the legs spread out in 

 the fashion of a spider. It is found in profusion, in summer, 

 on the Boleti and on Agarics, growing in plantations. The 

 mite lives about the root of the i'ungus, and many were nes- 

 tled in excavations made by slugs in the stalk.* 



In my search for the name of this mite I found three spe- 

 cies in the Systema Naturae, viz., the Acarus coleoptratus, 

 geniculatus, and tremellae, to which it was evidently nearly 

 related. They belong to the genus Oribata of Latreille, and 

 this author has described with greater fulness two of these 

 species, but his descriptions, I remarked, do not coincide with 

 the short Linnaean characters. Linnaeus says of his Ac. pent- 

 culatus that it is black, with the joints of the thighs subglobose ; 

 whereas Latreille's character, correctly translated by Leach, is 

 ** brownish-red, shining and hairy ; feet pale-brown ; thighs 

 rather clubbed." The Linnaean character of Ac. coleoptratus 

 again is, — " A. ater, lateribus nigro-subcoleoptratis \' — that 

 of Latreille, " 0. abdomine obscure castaneo, glaberrimo ; 

 lateribus solute alatis." — The extended description of the Ac. 

 coleoptratus in the Fauna Suecica proves it to be distinct from 

 the insect before us ; and I had therefore concluded that the 

 Ac. geniculatus of Linnieus was before me, when Latreille's 

 authority made me halt. 



Again on the search, I ascertained that no one of the seven 

 Oribatae described by Latreille was identical with ours ; and 

 of those figured in Griffith's edition of the " R^gne Animal," 

 the only one to which it bore a resemblance, was the O. cla- 

 vipes, pi. 23, fig. 6. There were, however, sufficient differences 

 between the living animal and the portrait to show that 



* I have found this mite on Boletus scaber and luteas, ou Amanita mu6ca> 

 ria, and on two or three Agarics in Juno and July. It is alwajrs on the stalk 

 of the fungus, but two or three individuals had crept in between the gills of 

 the Agarics. 



