28l 



SOME BRITISH EARTHMITES. 



Trombidiidae . 



C. F. GEORGE, M.R.C.S. 



Johnstoniana errans. — This very remarkable mite was des- 

 cribed by Dr. George Johnston in his ' Acarides of Berwick- 

 shire His description, which is accompanied by figures of 

 the hairs of this mite on their bulbous base, one palpus, and 

 two parts of the hind leg, is so clear and minute, that there can 

 be no mistaking the identity of the creature. He describes it 

 as blood red, with scarlet thorax legs and palpi ; smooth to the 

 naked eye. He points out that it is not a characteristic 

 Rhyncholophns, but stands as it were between that genus and 

 Tvombidiiim. Now, dissection shews that it is nearer to 

 Trombidutm than to RhyncholophiLs ; for the great distinction 

 between these two genera is, that in Rhyncholophus the man- 

 dibles are straight and fitted for piercing, whilst in Trombidhim 

 they are sickle shaped, and adapted for tearing. Figure b. 

 is a mandible of this mite, and may be compared with that of 

 Tromhidium holosericeum (see page 333 of ' The Naturalist ' 

 for 1908, fig. i.). 



In ' The Naturalist ' for 1907, page 180, will also be found a 

 figure of the mandibles of Erythroeiis, which is one of the 

 Rhyncholophidce, and shews distinctly the great difference 

 between the mandibles of the two families. 



At present Tromhidium is divided into two sub-divisions, 

 viz., Tromhidium and Ottonia, and as the specimen now being 

 described differs so greatly from both of them, I have ventured 

 to make it a third sub-division, which I call Johnstoniana. It 

 differs from the two other sub-divisions as follows : — 



(a) The body is longer than broad, only very slightly wider 

 at the shoulders, the sides are straight and almost parallel, 

 and the posterior end is widety and regularly rounded. 



{h) There is a distinct mark of division between the body 

 and the cephalothorax ; the latter is conical, and pointed in 

 front. 



[c] The eyes, each of which has two ocelli, are raised on 

 short pedicles, and situated on the upper side of the cephalo- 

 thorax, but wide apart. 



(d) The palpi, one of which is drawn much enlarged (fig. c), 

 besides the large claw at the end of the fourth joint, have two 

 accessory smiall claws. Tromhidium has no accessory claw, 

 and Ottonia only one. These accessory claws are made out 

 with difficulty, but can best be seen b\^ examining the palpi 

 before the mite is mounted. 



* ' The Berwickshire Naturalists' Club Transactions,' Vols. 11. and III, 

 1909 Aug. I. 



