342 TWO SPECIES OE PARASITIC MITES, 
female, and not that the female was degraded by more complete 
parasitism from a mite possessed of the higher type of structure 
presented by the male ; thus the nymph or unimpregnated female is 
very much like the adult female, except that it is slightly smaller, 
and there is no ventral opening to the oviduct, and the larva also is 
very like the female, except that the fourth pair of legs have not yet 
appeared. The egg is more or less irregularly, oval in shape, and 
somewhat more than half as long as the adult female. 
It will be seen from the above description that the mite found on 
the ear of the mouse differs considerably from any forms already 
described, resembling Dermatoryetes fossor (Ehlers) in the simple 
character of the female, but resembling much more nearly Myobia 
musculi in the structure of the rostrum and the general form of the 
male. It also differs from D. fossor in being oviparous and not 
viviparous. 
Considering all the circumstances, it has appeared to me advisable 
to create for its reception a new genus, with the following characters: 
PSORERGATES, 7. g. 
VYwpa, a scab; épyatys, a builder. 
General shape of the male and female quite different, the male 
being provided with legs which are terminated by a spine and 
claw, in the female the legs are very small and without termina] 
appendage, Mandibles styliform. The nymph and larva resemble 
the female rather than the male, Oviparous. 
PSORERGATES SIMPLEX, 7. sp. 
Characters enumerated above. 
Its habits were mentioned in the first part of this paper, namely, 
that it has been found living under a soft scab for the most part 
inside the conch of the ear of a mouse (Mus musculus) ; but atten- 
tion must be drawn to the circumstance that the male, though very 
active, and often found on the surface of the scab, must also bore 
into and under it in order to copulate with the nymph, which, from 
the shortness of its legs, would be unable to move outside the tissues 
of its host. In this particular it differs essentially from Sarcoptes 
minor, in which it will be remembered the nymph is active and 
moves about on the surface; and it is only after copulation that it 
bores into the tissue and assumes the adult form. 
