THE GAMASID^. 97 



The Gamasid.^ form a family of the order Acaridea, class 

 Arachnida^ and are found sometimes on the ground in damp 

 places, and sometimes parasitic on animals. 



One of the commonest is that so often seen on beetles, partic- 

 ularly on those of the genus Geotrtipes, though it attaches itself 

 to Humble Bees and other insects. It was named by Linneus 

 Acarus coleoptratorum (Fig. i). 



Of the Linnean genus Acams, Latreille formed a family, the 

 AcaridicB, and divided it into five genera : Tromhidium^ Ery- 

 t/irtTus, Gamasus, Oribafa, and Acarus ; and of his third genus, 

 Ga7?iasus, he made Coleoptrato7-u7]i the type. 



Of these five genera, Duges (1834) took one, Latreille's genus, 

 Gamasus^ and made this into a family, the GamasidcB, which he 

 again sub-divided into five genera : Derjiianyssus^ Gafnasjis, 

 Uropoda, Fferoptiis, and Argas. \\'\i\\ only two of these genera, 

 however — namely, Gamasus and IJj-opoda — I am now concerned. 



Up to the last ten or a dozen years, great confusion existed in 

 the classification of these two genera, which confusion is not as 

 yet completely cleared up ; for Duges, Latreille, Degeer, and even 

 Linneus, took for types of species, and occasionally even of 

 genera, sometimes the males, sometimes the females, and some- 

 times the simple nymphs; and in 1876, M. Megnin published a 

 paper to show that Gamasus Coleoptratorum of Latreille and of 

 Duges — the old Acarus Coleoptratorum of Linneus — was merely a 

 nymph — that is, an individual imperfect and without sex ; and 

 that the division of the dorsal plate into two parts {^vide Fig. i), 

 which had been taken as a special characteristic of the genus 

 Gamasus^ would disappear when the mite was full grown ; that 

 G crassipes was the male * and G testudinarius the female of the 

 same species of which G. Coleoptratorum was the nymph. 



I have a small beetle of, I think, the genus Hister, which one 

 of my children caught in the garden and brought to me. It is so 

 completely covered with these Gamasids that I could not deter- 

 mine its species without removing them, which I was unwilling to 

 do. The beetle, although its body is almost hidden by the mass 

 of parasites, does not appear to be any the worse for it, and runs 



* Mr. A. D. Michael considers that in regard to G, crassipes M. Megnin is 

 mistaken. 



Journal of Microscopy and Natural Science. k 



New Series. Vol, II. 1889. 



