128 ARACHNOIDEA. 



CASE Pachygnathus velatus {Dug., Ann. Sc, Nat. 1834). — 8. Magnified sketcb 



^^- of ditto. 



No. 8. 



Pachygnathus velatus. Copied from Dug^s' figure. 



Brick-red, body like that of Smaridia. Found by Duges in con- 

 siderable numbers under moist stones. 



Genus Trombidium {Fab). 



The chief distinguishing characters of this genus is that the 

 body is divided into two parts ; one small, anterior and inferior,, 

 bearing the eyes, the mouth, and the two first pair of legs ; the 

 other much larger, swollen and velvety, and bearing the two last 

 pair of legs. The two anterior and two posterior pairs are thus 

 at some distance from each other, as shown in the woodcut of the 

 under side of Trombidium holosericeum. 



The legs are seven-jointed, and, like all the other mites whose 

 development has been traced from the ^gg, the early stage of the 

 life of the harvest mites is passed in a form not unlike the mature 

 insect, with the exception that the posterior pair of legs is wanting. 

 These six-footed mites were by the earlier observers supposed to 

 be species of different genera of a division of the Acaridse, which 

 they designated Microphthiridae, possessing only six feet, and the 

 different types received different generic names. Three of these 

 belong to the present group, viz.: — Leptus, Ocypetus, and Atoma. 

 Achlysia belonged to the Hydrachnidae, and Caris was the larva 

 of Argas. 



