232 ARACHNOIDEA. 



CASE perfectly still, but when touched, began to run with much quick- 

 ness. Their colour was reddish ; the body oval, and the head 

 furnished with a little trumpet, in front of which were several 

 rather long hairs. The first two pairs of legs were large, the third 

 much shorter, and the posterior very long and filiform. Linnaeus, 

 after this author, described it in his " Systema Naturae," under the 

 name of Acarus muscarum ; Geoffrey, who seems also to have 

 seen it, called it the brown Fly-mite. This was the first notice we 

 have of the Hypopus. 



Subsequently, in April, 1797, Hermann found in great numbers, 

 on the underside and feet of a larva of a Lamellicorn beetle (Os- 

 moderma eremita), very small, oval, fleshy mites, of a brownish 

 yellow, with short stiff feet, and the tarsus with prickles bent 

 outwards, which he called spinitarsus (Acarus spinitarsus). 



Duges, long afterwards (in 1834), found on a Hister an Acarus, 

 which he thought was identical with that of Hermann, and made 

 a genus (Hypopus) for it, to which he transferred the Acarus 

 muscarum of De Geer, and which he thus characterised in placing 

 it in his family of Acarus. " These Acarids have a narrow 

 sucker, provided with two rigid bristles, directed outwards, and 

 seeming to be composed of a lip soldered to the palpi." He 

 adds, that the mandibles were not seen by him. By the crushing 

 of the only specimen he had in his hands, he saw that the anterior 

 bristles started from a moveable part, in the form of a parallelo- 

 gram, membranous in the middle, and thick at the edge, like the 

 lip soldered to the palpi in the Acarids, properly so called. He 

 could find no other palpi, nor perceive the mandibles. 



Leon Dufour, in 1839, discovered two other species of this 

 genus ; the one (H. feroniarum), lived in crowded groups under 

 the head, corslet, and abdomen of beetles belonging to the genus 

 Feronia; the other (H. sapromyzarum), lived on diptera of the 

 genus Sapromyza. 



Thereafter, Dujardin, in 1843, described an Acarus, which 

 from the mouth and abdominal suckers, cups, or sucking appa- 



