SOME PARASITIC ACARI. 
403 
ward, while the abdomen is somewhat raised ; thus the creature 
has the appearance of possessing caput, thorax, and abdomen. 
The abdomen has two very long hairs at its hinder end, and there 
are two smaller, but still large, hairs on the lateral edge between 
the second and third legs ; and two on the cephalothorax, as iu the 
other species, besides two sparse longitudinal rows of smaller 
hairs on both divisions of the body. The first and second legs 
are like those of the male, but the claws are shorter. The third 
and fourth legs resemble the third pair of the male, but the claws 
again are shorter, but, on the other hand, they are broader. 
These great holding-claws in this species are much wider iu pro- 
portion than those of M. musculinus ; indeed, their breadth is 
very remarkable. On the ventral surface the epimera of the first 
pair of legs join in the median line and are prolonged by a short 
sternum (so-called) ; those of the second pair of legs are forked 
at their distal ends. Posterior to these, and almost touching those 
of the third pair, are two conspicuous chitinous pieces of rather 
more than half-a-circle shape with their outer corners slightly 
prolonged ; the chitinous pieces protect the vulva, which lies 
between the third and fourth pairs of legs. 
The Nympli . — The nymph is very similar in form to the male, 
but without the square posterior projections ; there is only one 
pair of large bairs posteriorly. The fourth pair of legs are similar 
to the third, as in the female. The constriction between cephalo- 
thorax and abdomen is very marked. Neither pair of legs are 
nearly so long as the third pair of the male. 
The Larva . — Almost diamond-shaped ; of course there are not 
any fourth legs, but the third pair are placed near the posterior 
end of the body, giving a very singular appearance. Otherwise 
the larva resembles the nymph. Both differ considerably from 
those of M. musculinus. 
Habitat. Parasitic upon the field-vole ( Arvicola agrestis). 
Symbiotes tripilis, n. sp. (PL XXVI. fig. 8.) Female. 
mm. 
Length about - 33 
Breadth about '26 
Length of legs : 1st and 2nd pairs about T5 
3rd pair about 06 
4th pair about - 03 
Length of longest hair on 3rd tarsus about ‘70 
on hind margin of body about ’40 
