10 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. 62. 
Iowa. On two of the five slides in the United States National 
Museum are the mouth parts dissected so as to show their nature to 
a better advantage. 
Genus TETRAGONYSSUS Ewing. 
KEY TO NORTH AMERICAN SPECIES. 
a’. Species larger and much more heavily spined; at least one pair of spines on 
femur I almost half as long as front legs; and plate fully twice as long as broad. 
anus with an even but enormously thickened rim, anal setae minute. 
T. spiniger (Ewing and Stover). 
a?. Speciessmaller and much less heavily spined; longest spine of femur I less than 
one-third the length of leg I; anal plate subtriangular and about as broad as 
long, anus with an uneven and but moderately thickened rim, anal setae large 
spines which almost reach the tip of anal plate... T. bermudaensis (Ewing). 
TETRAGONYSSUS SPINIGER (Ewing and Stover). 
Female.—Large and spiny. Palpus and chelicera rather small; one 
of the arms of the latter longer than the other. Above the body is 
sparsely clothed with short spines, those toward the front being re- 
curved and along each side there is a row of longer spines. Peritreme 
very sinuous and extending to opposite the anterior coxae. Sternal 
plate very large, longer than broad, and reaching the fourth coxae. 
Anal plate twice as long as broad, and broadly rounded in front; anus 
oval in outline, rim almost as broad as anal aperture and of even 
thickness; anus itself situated almost entirely in front of the middle 
transverse line; paired setae, minute, situated on rim of anus; median 
seta large and situated on a low tubercle at base of caudal area, the 
latter being triangular and scobinate. Legs stout, especially the first 
two pairs; dorsal spines of femur I two in number, the outer situated 
on a tubercle and enormous, being half again as long as the inner. 
Length, 0.78 mm.; width, 0.51 mm. 
Male.—Considerably smaller than the female. Dorsal shield large 
but short, broadly rounded behind and not extending beyond the 
middle of abdomen, sides convex. Holoventral plate very much 
produced between the second and third coxae and expanded on the 
abdomen, with the following spinelike setae: A pair on either side of 
genital opening; a pair opposite second coxae and another opposite 
third coxae; a pair situated on a level between the third and fourth 
coxae and six pairs on abdominal part of plate. Genital opening 
somewhat funnel shaped with well-developed rim. Anus almost 
circular, situated about twice its greatest diameter from the poste- 
rior margin of holoventral plate. Length, 0.65 mm.; width, 0.38 mm. 
Type locality.—Ithaca, New York. 
Type.—A single female, the uppermost specimen on type slide, is 
here designated as type. 
