24 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. 62. 
as long as median setae; caudal area a slender marginal crescent. 
Legs large; anterior and posterior pairs longer than the others; 
tibia I slightly over twice as long as broad. Length, 0.69 mm.; 
width, 0.40 mm. 
Male.—Much smaller than most of the females. Chelicerae each 
with the following armature: Two long, sinuous, tapering and adhering 
elements, one which surpasses the other with its distal, setiform, 
hooklike terminal portion; and a short spinelike, or styletlike, pro- 
cess, the latter probably representing the fixed chela. Dorsal shield 
similar to that of the female but more slender, more rounded at the 
posterior margin, and extending for almost the entire body length. 
Holoventral plate almost equally expanded into cusps between the 
first and second, second and third, third and fourth coxae. Anus 
situated less than its greatest diameter from the posterior margin of 
holoventral plate. Length, 0.61 mm.; width, 0.32 mm. 
This species is probably present in all localities all over the world 
where chickens are raised to any extent. The following American 
hosts are known: Chickens, canaries, pigeons, English sparrows, and 
towhee (2). The species annoys also all domestic animals and man, 
but seldom attacks a mammalian host. 
DERMANYSSUS AMERICANUS, new species. 
Female.—Palpi extending to beyond the tips of the anterior femora; 
chelicera showing the two elements (arms) quite distinctly. Peri- 
treme very short, not extending beyond third coxa; it is almost 
straight and is slightly bulbous near the stigmal opening. Sternal 
plate (apparently) crescentic and with three pairs of long, subequal 
setae. Anal plate slightly longer than broad, broadly rounded both 
in front and behind; anus with longitudinal diameter almost twice 
as great as transverse, rim thin in front, thicker on the sides, and 
very thick behind. The anus is situated almost entirely behind a 
middle transverse line; paired setae situated slightly behind the 
level of the anterior margin of anus; caudal area a narrow, crescen- 
tic area along margin of plate. Legs very short and stout; last pair 
falling far short of tip of abdomen. Length, 0.62 mm.; width, 0.36 
mm. 
Male.—Not known. 
Type locality—Washington, District of Columbia. 
Type (holotype).—Cat. No. 24754, U.S.N.M., the lower of the two 
specimens on type slide selected. 
Two individuals from English sparrow, Washington, District of 
Columbia, December 19, 1913, by R. S. Shannon. 
