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Genus Aponomma 
Eyes wanting. Anal groove surrounds anus pos¬ 
teriorly, and opens anteriorly. Anal plates absent. 
Base of rostrum pentagonal. Scutum covers the 
dorsum entirely ; usually marked with green spots. 
Stigmata, comma-shaped. Female, scutum shorter 
than broad, three green spots. The species are 
parasitic on reptiles. 
Genus Dermacentor 
Coxa IV very large. Eyes present. Base of 
rostrum broader than long. Palpi short and thick. 
Stigmata, comma-shaped. Anal shields absent in 
male. Coxa I bidentate in S and ?. Scutum 
ornamented. About twenty-four species. 
(1) D. electus is the American dog tick. 
(2) D. occidentalis conveys c spotted fever 5 of 
the Rocky mountains, the cause of this disease being, 
however, unknown. 
Genus Ornithodoros 
Eyes present or absent. Rostrum hidden under 
a projecting beak (head) close to the margin of the 
body so that the tips of the palpi only are visible from 
above. Body generally oval, sides generally straight, 
skin mammillated throughout. Lateral margin not 
different as in Argas. No moveable plate on each 
side of palpi. 
(1) O. savignyi .—Has two pairs of eyes situate 
on a horse-shoe shaped elevation surrounding the 
base of the legs and the mouth parts. Hind tarsi are 
slenderer than in 0 . moubata. On the last segment 
of the hind legs are three knobs, the distance between 
the second and third three times as great as that 
