322 
ARACHNIBES. 
are very injurious to them. These particular species is reddisli, 
witli a blackish si)ot on each side of the abdomen. 
Cheyletus, Lat. 
Didactyle chelicerse ; but the palpi are thick, resemble arms, and 
liave a falciform termination *. 
Oribata, Lat. Notaspis, Herm. 
The chelicerae are also didactyle in the Oribatse, but their palpi 
are very short or concealed ; their body is invested by a firm, cori- 
aceous or scaly skin resembling a shield, and their legs are long 
or moderate. 
The anterior part of the body projects into a snout, and an ap- 
pearance of a thorax is often observable. The tarsi, in some, are 
terminated by a single hook, and in others by two or three, without 
any vesicular pellet. 
They ai’e found on stones, trees, and in moss ; their gait is slow |. 
Uropoda, Lat. 
Judging from analogy, we presume that the Uropodse are fur- 
nished with forceps-like chelicerae. Their palpi are not apparent ; 
their body, still covered with a scaly skin, has but very short legs, 
and a filament at the anus, by means of which they attach them- 
selves to certain coleopterous Insects, suspending themselves in the 
air J. 
Acarus, Fab. Lat. — Sarcoptes, Lat. 
Two didactyle chelicerae, and very short or concealed palpi, as in 
the preceding; but the body very soft or without a scaly crust. 
The tarsi have a vesicular pellet at their extremity. Several spe- 
cies live on the food of Man, and others are found in his psoraic 
ulcers, and in those of the Horse, Dog, and Cat §. 
Others, called Ticks — Ricini^, Lat. — also have eight legs, solely 
adapted for running, but arc destitute of chelicerae, properly so 
called ; they are replaced, however, by two lancet-like blades, which, 
with the ligula, form a sucker. 
Sometimes they have distinct eyes, and salient, filiform, free palpi ; 
a sucker composed of membranous parts, and entire ; and a very 
soft body. They are errant animals. 
Bdella, Lat. L'ab. — Scirus, Herm. 
Elongated palpi, bent into an elbow, with setae or hairs at the ex- 
Acarus erudihts, Sdu-ank., Enum. Insect. Aust., No. 1058, Tab. II, 1; ejusil., 
peciculus miiscuU, Ib., No. 1024, I, 5. 
-f- See Hermann, Mem. Apter., genus Notaspis; and Olivier, Encyc. Method., 
Insect., article Oribate. 
Acarus vegetans, He Geer, Insect., VII, vii, 15. The Acarus spinitarsus, Herm. 
Mem. Apter. VI, vi, 5, perhaps forms a genus intermediate between this and the 
preeeding one. 
§ Acarus domesticus,De Geer, Ib., V, 1 — 4; — Acarus siro, Fab. ; — Ac. scabiei, Ib., 
12, 1.3. See the dissert, of Dr. Galet ; — Ac. farina, Ib., 15; — Ac. avicularum, Ib., 
VI, 9 ; — Ac. passerinus, Ib., 12, remarkable for the size of its third pair of legs ; — 
Ac. dimidiaius, Herm., Mem. Apter. VI, 4 ; — Trornbidium expalpe, Ib., II, 8. 
