638 Mr. E. Saunders' Synopsis of 



A A. Thorax entirely black. 



B. Very wide across the region of the intermediate 



coxjB; posterior tibisD and tarsi together as long 



as the femora glbUfera. 



BB. Not very wide across the region of the intermediate 

 coxa;; posterior tibia; and tarsi together not so 

 long as the femora. 



C. Posterior tibia; and tarsi together not quite so 



long as the femora. 



a. Anterior femora chiefly Intcons, $ with 



the abdomen not toothed beneath . . lacustris. 



b. Anterior femora black, red at the extreme 



base ; sixth segment of abdomen toothed 



beneath, in ^ . . . . . . . . odontogaster. 



CC. Posterior tibi.a" and tarsi together about two-thirds 



the length of the femora . . • . . . argentata. 



1. riifoscutellata, Latr. Fig. H.-Schff. Wanz. Ins. ix. 



pi. ccc. fig. 924. 



Head black. Thorax rufescent, with a paler central 

 line and a dark spot on each side of it near the anterior 

 margin. Elytra brownish; the costje black and the inter- 

 stices whitish in their centres; legs and antennae rufescent 

 beneath, covered with silvery, — in some light golden, seri- 

 ceous hairs. 



Length 6^ lines. 



Carlisle. 



2. pallidum. Fab. Fig. H.-Schff. "Wanz. Ins. ix. pi. ccc. 



fig. 926. 



Entirely black above, except the edges of the abdomen ; 

 beneath silvery white. Thorax Avith a fine narrowly-raised 

 central line; posterior angles somewhat prominent. Pos- 

 tei'ior femora distinctly longer than the tibia? and tai'si 

 together. First joint of the antennfc not quite so long as 

 the other three together. 



Length 6 — 6.3 lines. 



Ponds, &c., rare; Caterham, Eltham, &c. 



3. Najns, De Geer. Fig. Il.-Schff. "Wanz. Ins. ix. 



pi. ccc. fig. 925. 



Very like the preceding, but more elongate and gene- 

 rally Avithout elytra. Posterior femora scarcely longer than 

 the tibia3 and tarsi together. Fu'st joint of the antennje 

 as long as the other three together ; it may also be dis- 

 tinguished by the characters given in the table at the head 

 of the genus. 



Length 6 — 6^ lines. 



Common on running water, &c. 



