HARVEST MITES, 129 



CASE Trombidium parasiticum (Atoma parasiticnm, Latr.). — 9. Magnified 

 ^^* sketch of under-side of ditto, copied from Riley's Seventh Missouri 



No- 9. Report. 



Latreille, in establishing a genus for this mite, ^ ^. . 



proposed the name Atoma for it, by which we ^"^^^f^,/ 



suppose he meant an atom ; but he subsequently , lJ-A-LJ 



(in 1806) altered it to Astoma. It may be more ^ff^ -^ 



euphonious, but is not so correct, Astoma mean- \~^ 



ing without a mouth, which is certainly not the 



Atoma parasiticum. 



case with this creature. The alteration has not 



been universally adopted (Duges, for example, still calls it Atoma 



in 1834), and seeing that the rigid rules of priority admit (for 



there seems no good reason under it why the author of a name 



should have the right to change it subsequently any more than 



any one else), we shall stick to the first name for the reason above 



given. 



The creature to which the name was given is a minute blood- 

 red mite, parasitic on the house-fly. In this country they do not 

 seem so prevalent, but Mr. Riley mentions that in North 

 America in some seasons scarcely a fly can be caught that is not 

 infested with a number of them clinging tenaciously round the 

 base of the wings. 



It is only six-footed, consequently we may be certain that it 

 is the larva of some other species, probably of Trombidium, 

 although what species has not yet been ascertained. 



Nos. Trombidium holosericeum {Fab.), (T. phalangii, Duges' s Ann. Sc. Nat. 



X2,\i, 1834). — 10. Magnified figure of young ; 11. Magnified figure of perfect 



insect, agreeing with Duges's figure, and No. 13 ; 12. Specimen of 

 perfect insect in microscopic slide ; 13. Magnified figure of perfect 

 insect as figured erroneously by Walckenaer and others. 



This also is a species that in its young stage is parasitic on 

 another insect. It is then found adhering to the long-legged 

 harvest spider, Phalangium opilio, and there is no doubt as to its 

 transformations, Duges having carefully observed them. He 



