DB. JOHNSTON ON THE ACARIDES OF BERWICKSHIRE. 303 



This mite frequents the same places, and infests the same 

 beetles as the G. coleoptratorum, which it equals in size ; nor 

 am I aware of any peculiarity in its habits. There are, how- 

 ever, some unessential differences in the oral organs, which 

 it is impossible to describe intelligibly without the aid of 

 figures ; nor do I think that specific characters can be derived 

 from them. It is a common mite, and yet I am at a loss to 

 discover whether it has been described. The character of 

 Acarus coleoptratorum, given by Linnaeus — " A. rufus, ano 

 albicante," — suits it well, but the description in the Fauna 

 Suecica proves that the name has been rightly appropriated to 

 a species equally common. Ours is surely what has been usually 

 named in British lists Gamasus marginatus, but it is not the 

 G. marginatus of Latreille, " pedibus anticis corpore duplo 

 longioribus," — the anterior legs being scarcely if at all longer 

 than the body ; nor is it the G. marginatus of Leach, in which 

 the anterior legs are " nearly twice as long as the rest" (Ed. 

 Encyclop. viL 415), for in the insect before us it requires a 

 nice eye to say that they are longer than the posterior pair. 

 Dugi^s has described a G. marginatus (Gamase bord^^) which 

 is more closely allied to our species, but they seem to differ 

 in the shape and character of the sternal plate, and in the 

 colour of the chelae of the mandibular arms, which are stated 

 to be " noiratre." In our species they are yellowish-brown. 

 — I am thus driven on to conjecture, for I have not access to 

 works in which any related species are described. Acting 

 under the belief that such a common mite cannot have escaped 

 notice, I refer it to the Acarus testudinarius of Hermann. 

 Latreille says that this is allied to Gamasus marginatus ; and 

 Dugcis tells us that it differs very little from his Gamase bor- 

 d^. Gervais has merely mentioned the name. Koch places 

 it in a different section of the genus from G. marginatus, but 

 in the one immediately following and not far distant, — a 

 view which rather strengthens the truth of my conjecture. 

 It must, however, be remarked that the mite has nothing in 

 common with the Acarus testudinarius of Schranck, 



13. Gamasus marginatus. 

 G. ovatus bruiiueus supra infraque coriaceus abdominis 



