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, 71. g. 



Wiopa, a scab ; ipyarTjs, 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 terminal 

 appendage, Mandibles styliform. The nymph and larva resemble 

 the female rather than the male, Oviparous. 



PSORERGATES SIMPLEX, 71. 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. 



