AC ARID S. 227 



Family ACARIDiE. 



Authors have hitherto been in the habit of including in one 

 division, called Sarcoptidae, the whole of the old genus Acarus, or 

 soft-bodied semi-transparent fleshy mites. By far the larger 

 portion of these seems to us, however, to be capable of division 

 into two tolerably distinct and easily distinguishable sections- 

 One, the cheese mites and their aUies (Tyroglyphidae), and the 

 other the Sarcoptidse, Itch mites, and their relatives the louse mites. 

 This, however, does not exhaust the list of those usually ranked 

 under the Sarcoptidae. There arc at least three minor groups, the 

 Hypoderlds, the Hypopidse, and the Phytoptidae, which are all so 

 peculiar in their appearance and mode of life, that we propose to 

 rank them as separate secondary sub-divisions. We would suggest 

 as a cemvenlent arrangement that the whole of the old genus 

 Acarus should be divided into the following sub-families — viz. : 



1st Section. — Surface of skin smooth, shining or velvety; tarsi usually with 

 claus. 



1. Hypoderidas. — Long bodies and very short legs, with a great distance 



between the two anterior and tw«> posterior pairs ; parasitic under 

 the skin of birds ; mouth not made out. 



2. Hypopida. — Without any apparent mouth ; anterior pair of legs 



generally much developed ; posterior often almost atrophied, 



3. Tyroglyphidse. — Cheese mites, with chelate mandibles and stout legs, 



and the tarsi in some with and others without a sucker, 

 ind Section. — Surface af skin more or less transversely striated; tarsi usually 

 with suckers instead of claws. 



4. Sarcoptidae. — Itch mites, which are rounded or quadrate, with legs 



short and feeble; and Dermaleichidoe. — Louse mites, usually elon- 

 gate, and often with some of the legs monstrously developed. 



5. Phytoptidae. — Gall and bud mites. 



We know that no definition can be given which will absolutely 

 and sharply separate any group of insects, but the above charac- 

 ters will, we think, answer the purpose of a natural arrangement, 

 provided a few transitional exceptions on either side be allowed. 

 The species of the first group, Hypoderldae, are internal parasites ; 

 the next group, Hypopidae (as we believe), are Ichneumon para- 



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