1877.] MR. G.S. BRADY ON BRITISH FRESHWATER MITES. 27 
Family Acarip2&. 
Genus ScuisTosoma, nov. gen.’ 
In general appearance resembling Sarcoptes ; posterior portion of 
the body divided into two wide triangular processes ; two hinder feet 
entirely different in structure from the anterior pairs, and projecting 
directly backwards from the back of the body, the anterior legs also 
arise from the truncate anterior margin of the body. 
ScHISTOSOMA LONGISETOSUM, nov. sp. (Plate III. fig. 1.) 
Body subquadrate, truncate in front ; rostrum obtuse and promi- 
nent, posterior extremity divided into two triangular pointed laminz, 
each of which bears several terminal setze, one pair of which is exces- 
sively long; near the centre of each lamina is a circular organ, not 
unlike the caudal auditory organ of Mysis. The two anterior pairs 
of legs are short and robust, each bearing a few setz and one or two 
marginal spines. The terminal joints of the posterior legs are divided 
into several slender segments and are destitute of claws; those of the 
third pair bear one very long and a few smaller sete; the anterior 
legs terminate apparently in delicate suctorial disks. Behind the 
rostrum arise, one on each side of the median line, two long sete 
which project first laterally and then forwards, reaching nearly to 
the extremities of the feet. Several pairs of somewhat shorter setze 
arise from the margins and central portion of the body. The animal 
is pale coloured; and the integument appears to be less dense and 
horny than in most aquatic Acari. No eyes were visible. Length 
sy of an inch. 
One specimen only of this remarkable species was noticed in a 
gathering of Hatomostraca taken by Mr. Robertson in an old canal 
at Peterhead. 
EXPLANATION OF THE PLATES. 
Puate III. 
1. Schistosoma longisetosum, magnified. 
2. Raphignathus spinifrons, magnified. 
3. The same. Rostrum, palp, and portion of front of carapace. 
a. Rostrum; c. Margin of anterior portion of carapace; 6. Palp. 
4, Mandibles. 
5. Extremity of a foot, with claws. 
Puate LY. 
1. Rhyncholophus hispidus, magnified. 
2. Extremity of palp. 
3. Extremity of foot, with claws. 
4, Pachygnathus nigrescens, magnified. 
5. Extremity of foot, with claws. 

1 oyiZw, to split; cdma, body. 
