366 Dli. JOHNSTON ON THE ACARIDES OF BERWICKSHIRE. 



coriaceous region of the same colour and texture as the ster- 

 nal plate and the back : Rostrum triangular, acuminate : 

 Mandibles large and protrusile, the shaft two-jointed, and 

 armed with chelae ligfitly tinted with brown : Palpi large, 

 5-jointed, spinous, tapered, the penultimate joint rather long- 

 est and armed with a moveable spine, the terminal small, 

 rounded and setigerous : Legs 8, originating near the sides 

 from the anterior half of the venter, approximated at their 

 insertions and almost equally distanced, stout and tapered, 

 spinous, of the colour of the body with paler articulations, 

 6-jointed ; 1st joint short and thick, 2d small, Sd, 4th, and 

 5th as long as both together, and progressively increasing a 

 little in length, 6th nearly twice as long as the penultimate, 

 tapered and terminated with a pedicled vesicle ; the ante- 

 rior pairs are ratlier thicker than the posterior, not very un- 

 equal in length, but the first pair is longest, the second and 

 fourth equal, and the third shortest; the 3d joint of the first 

 pair is much constricted at its articulation with the 2d joint ; 

 Bristles setaceous, pointed downwards, longer than the dia- 

 meter of the joint, barbed with minute spinules on one side. 

 D. musculi is equal in size to the Gamasus coleoptratorum. 

 Numerous specimens occurred on the same field mouse which 

 furnished those of the Laelaps and Pfceroptus, about to be de- 

 scribed. It is exceedingly active, and courses over the body 

 of its victim with great rapidity. 



23. Pteroptus muris. 



Pt. albus, corpore accurate ovato antice trisinuato sparse 

 setoso, pedibus anticis crassioribus. 



Desc. Mite minute, of a white colour with irregular duskier 

 shades, the legs of the colour of the body : Body ovate, spa- 

 ringly covered with short setaceous bristles, even, the frontal 

 margin trisinuated or obsoletely 3-lobed, and sinuated on the 

 sides a little behind : Mandibles forming together a porrect 

 rostrum situated between the palpi, each mandible consisting 

 of a two-jointed elongated protrusile shaft terminated with 

 two minute curved denticles : Palpi pediform, very slightly 

 tapered, with a rounded bristly apex : Legs 8, much shorter 

 than the body, the two first pairs stouter than the posterior, 

 the 1st rather longest, the 2d and 4th about equal, the 3d 

 shortest, but there is in respect of length little difference be- 

 tween them, and all are terminated with a pedunculated 

 -trumpet -shaped vesicle, furnished with two minute divergent 

 claws ; all the joints are short and not very unequal, the 



