322 ARACHNIDES. 



are very injurious to them. These particular species is reddish, 

 with a blackish spot on each side of the abdomen. 

 Cheyletus, Lat. 



Didactyle chelicerse ; but the palpi are thick, resemble arms, and 

 have a falciform termination *. 



Oribata, Lat. NoTASPis, Herm. 



The chelicerae are also didactyle in the Oribatae, 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 are found on stones, trees, and in moss ; their gait is slow |. 



Urofoda, Lat. 



Judging from analogy, we presume that the Uropodae are fur- 

 nished with forceps-like cheliceroe. Their palpi are not apparent ; 

 their body, still covered with a scaly skin, has but very short legs, 

 and a filament at the an\is, 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 — RicinIjE, Lat. — also have eight legs, solely 

 adapted for running, but are 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. Fab. — Scirus, Herm. 

 Elongated palpi , bent into an elbow, with setae or hairs at the ex- 



* Acmiis eruditus, Schrank., Enum. Insect. Aust., No. 1058, Tab. II, 1; ejusd., 

 peciculus miiscuH, lb., No. 1024, I, 5. 



■f See Hermann, Mem. Apter., genus Notaspis ; and Olivier, Encyc. Method., 

 Insect., article Oribate. 



J Acarus vegetans, De Geer, Insect., VII, vii, 15. The Acanis spinitar^us, Herm. 

 Mem. Apter. VI, vi, 5, perhaps forms a genus intermediate between this and the 

 preceding one. 



§ Acarus domes fia'.s,'De Geer, lb., V, 1 — 4; — Acarus siro, Fab. ; — Ac. scabiei, lb., 

 12, 13. Seethe dissert, of Dr. Galet ; — Ac. farina, lb., 15; — Ac. avicularum, lb., 

 VI, 9 ; — Ac. passerinus, lb., 12, rem.arkable for the size of its third pair of legs ; — 

 Ac. dimidiafus, Herm., Mem. Apter. VI, 4 ; — Trombidium expaipe, lb., II, 8. 



