444 ARACHNID A 



fourth legs, each being surrounded by a chitinous ring called the stig- • 

 mal plate or peritreme, which usually extends forwards a long distance; 

 the young mostly born with 3 pairs of legs: numerous species and about 

 18 American genera, some of the species being parasitic on insects, espe- 

 cially beetles, and on vertebrates, while many species use insects for 

 transportation; some lead a free life in moss and on the ground. 

 Key to the genera of Gamasidae here described: 



fli Free-living or attached to insects and rarely to vertebrates. 

 &i First pair of less inserted on one side of the mouth opening. 



Ci Leg with one claw ; female genital plate triangular 1. Gamasus 



Co Leg 1 without claws ; leg 2 thickened 2. Macrocheles 



ftj First pair of legs inserted in the same opening as the mouth parts. 



4. Uropoda 

 Cj Parasitic on birds 3. Dermanyssus 



1. Gamasus Latreille. Body usually flattened, with or without a 

 transverse dorsal suture; female genital plate triangular; male genital 

 pore on anterior margin of sternal plate: about 10 American species, 

 which live on the ground, among fallen leaves, etc., or on insects. 



G. coleoptoruin (L.). Length .6 mm.; transverse dorsal suture pres- 

 ent; 4 large spines projecting from the hinder end; anterior end trian- 

 gular; first pair of legs with sucking discs: on beetles. 



2. Macrocheles Latreille. Body elongate, with 

 no transverse dorsal suture; second leg enlarged, in 

 male curved and armed with teeth; mandibles very 

 thick; male genital pore on anterior margin of 

 sternal plate; first pair of legs without claws: 

 several species. 



M. mcestus Banks. Body reddish-brown and 1 

 mm. long, with 8 rows of clavate hairs above and a 

 few on the hinder margin: common in ants' nests. 



3. Dermanyssus Duges. Bird mites. Body 

 elongate and not distinctly constricted; hind legs 



Fig. 698— Derwanj/s- not reaching the hinder end; mandibles chelate in 



(Banks). male, long and piercing in female: parasitic on birds, 



especially domesticated ones; 1 American species. 



D. gallinae (DeGeer). Chicken mite (Fig. 698). Body .7 mm. 

 long, .4 mm. wide, pear-shaped and flat and reddish in color : the mites hide 

 during the day in the coop and at night attack the fowls and suck their 

 Idood, and are often a serious pest; they frequently attack dogs, cats, 

 and horses, as well as man. 



4. Uropoda Latreille. Body ovoid, with depressions on the under 

 side for the reception of the legs; mandibles very long and slender, and 

 chelate: on beetles, ants, and other insects; some are parasitic, but most 



