TRACHEARI;. 217 



Acarus, Fab. Lat. Sarcoptes, Lat. 



Two didactyle cheliceras, 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(l). 



Others, called Ticks Ricini^e, Lat. also have eight legs, solely 

 adapted for running, but are destitute of cheiicerae, 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- 

 tremity; four eyes; the posterior legs longest; sucker projecting in 

 the form of a conical or subulate rostrum. Found under stones, 

 bark of trees, and in moss. 



Bd. longicornis; dearies longicornis, L.; La Pince rouge, Geoff.; 

 Scirus vulgaris, Herm., Mem. Apter., Ill, 9; IX, S. Hardly 

 half a line in length; scarlet; the feet paler; sucker in the form 

 of an elongated and pointed rostrum; quadriarticulated palpi, 

 the first and last joint of which are the longest; the latter some- 

 what the shortest of the two, and terminated by two setae. Com- 

 mon in the environs of Paris; under stones(2). 



Smaridia, Lat. 



Distinguished from Bdella by the palpi, which are hardly longer 

 than the sucker, straight and without terminal setae; by the eight 

 eyes, and by the two anterior legs, which are longer than the others(3). 



(1) Acarus domesticus, De Geer, lb., V, 1 4; Acarus sir v, Fab.; Ac. scabiei, 

 lb., 12, 13. See the dissert, of Dr Galet; Ac. farinsc, lb., 15; Ac. avicularum, 

 lb., VI, 9; Ac. passerinus, lb., 12, remarkable for the size of its third pair of 

 legs; Ac. dimidiatus, Herm., Mem. Apter., VI, 4; Trombidium expalpe, lb., 

 II, 8. 



(2) Scirus longirosiris, Herm., Mem. Apter. VI, 2; & latirostris, lb., II, III; 

 S. setirostris, lb., Ill, 12; IX, T. 



(3) Acarus sambuci, Schrank, and perhaps the following Trombidia of Her- 

 mann; Tr. miniatum, 1, 7; Tr. papillosum, II, 6; Tr. squammatum, lb., 7- 

 The second is even closely allied to the species which serves as a type to the 

 genus. 



Vol. III. 2 C 



