322 



AUACHNIDES. 



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

 with a blackish spot on each side of the abdomen. 

 CHEYLETUS, Lat. 



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

 have a falciform termination *. 



ORIBA.TA, 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 f. 



UROPODA, Lat. 



Judging from analogy, we presume that the Uropodae 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 RICINUE, 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 Hgula, 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. 



B DELL A, Lat. Fab. SCIRUS, Herm. 

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



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

 peciculus musculi, Ib., 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 Acarus spinitarsus, Herm. 

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

 preceding one. 



Acarus domesticvs,De Geer, Ib., V, 1 4; Acarus siro, Fab. ; Ac. scabiei, Ib., 

 12, 13. Seethe 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. dimidiatus, Herm., Mem. Apter. VI, 4 ; Trombidium expalpe, Ib., II, 8. 



