444 



AEACHNIDA 



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

 nial plate or peritrerne, 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: 



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

 &! First pair of legs inserted on one side of the inouth opening. 



G! Leg with one claw ; female genital plate triangular 1. GAMASUS 



c 2 Leg 1 without claws ; leg 2 thickened 2. MACBOCIIELES 



& 2 First pair of legs inserted in the same opening as the mouth parts. 



4. UROPODA 

 a a Parasitic on birds 3. DEBMANYSSUS 



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. coleoptorum (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. DEEMANYSSUS Duges. Bird mites. Body 

 elongate and not distinctly constricted; hind legs 

 not reaching the hinder end; mandibles chelate in 

 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 

 blood, 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 



Fig. 698 Dermanys- 



sus gallinae 



(Banks). 



