6 PROCEEDINGS OF THE NATIONAL MUSEUM. VOL. 62. 
CERATONYSSUS, new genus. 
Chelicera shearlike, being provided with both arms; hypostome 
without recurved hooks; basal segment of palpus of female with a 
hornlike process; dorsal shield of 
female divided, the posterior shield 
being large and about as long as the 
anterior. 
Type species.—Ceratonyssus musculi 
(C. L. Koch). 
The employment of sexual charac- 
ters for distinguishing genera has its 
objections, and under most conditions 
such characters should not be used. 
In the Gamasoidea, however, where 
the sexes are so different and where 
other characters than those of one sex 
only are hard to find, or for purposes 
of generic distinction do not exist, 
there is ample justification for the 
Fic. 3.—IXODORHYNCHUS LIPONYSSOIDES, practice. 
NEW SPECIES. VENTROLATERAL VIEW OF Besides the type, this genus in- 
ae in cludes Liponyssus javensis Oudemans 
and Ceratonyssus ceratognathus, new species, to be described in this 
paper. 
SERPENTICOLA, new genus. 
Chelicerae as in Liponyssus. Dorsal shield of female divided, the 
posterior shield being minute and subcircular; sternal plate of female 
with only four setae; basal segment of palpus in female without horn- 
like process; anal plate of female as in bird infesting Liponyssus 
species. 
Type species.—Liponyssus serpentium (Hirst). 
Only a single species included in this genus. It parasitizes Ameri- 
can snakes. 
TETRAGONYSSUS, new genus. 
Chelicerae as in Liponyssus. Body large and in the type species 
squarish behind and with pronounced shoulders in front. Dorsal 
shield entire and completely covering the body in both sexes; legs 
stout, spined above; sternal plate of female large, reaching third 
coxae; ventral plate of male quadrangular in front. 
Type species.—Liponyssus gigas Oudemans. 
Besides the type two other species should probably be included in 
this genus, L. spiniger Ewing and Stover and L. bermudaensis Ewing. 
