BIDESSUS. 23 
Hab. Muxico, Oaxaca (Hége). 
This species should be placed between groups 4 and 5 of my memoir; for it has the 
small coxee of the former, but the other characters are rather those of the latter of these 
groups. I have only two individuals before me; they are no doubt females, although 
they have the tarsi moderately broad ; they are extremely similar to the opaque female 
form of Dytiscus unistriatus, Schranck, but are much larger, and the punctuation of the 
metasternum is wanting. ‘The elytral stria is very distinct, and is about as long as that 
on the thorax. 
11. Bidessus affinis. 
Hydroporus affinis, Say, Tr. Am. Phil. Soc. i. p. 104. 
Hydroporus emilianus, Clk. Ann. & Mag. Nat. Hist. ser. 3, x. p. 183°. 
Hydroporus charlottii, Clk. loc. cit. p. 182. 
Hab. Norra America, from Sitka and Canada southwards.—MExico }; GUATEMALA.— 
Soutn America to Chili and Buenos Ayres. 
This widely distributed species shows many variations. The specimens from Mexico 
are smaller and more finely punctate than those from Guatemala, and are of obscure 
reddish colour, but exhibit a good deal of variation: it was on such specimens that 
Clark founded his Hydroporus emilianus; but there are no characters by which it can 
be distinguished from some of the North-American varieties. ‘The individuals from 
Guatemala approach to a variety found in Nevada, North America. 
12. Bidessus subornatus. 
Oblongo-ovalis, minus angustus, subtiliter pubescens, fuscus, antennarum basi, pedibus prothoraceque testaceis, 
hoc basi fusco; elytris subtiliter punctatis, parce sed longius pubescentibus, plica basali sat elongata 
profunda, signatura transversa subbasali alteraque apicali obsoletis testaceis ; corpore subtus fere 
impunctato, parcius pubescente. ' 
Long. ?—3, lat. vix 3 lin. 
Hab. Mexico, Oaxaca (Hoge); GuaTemaLa, San Gerénimo (Champion). 
Head impunctate in front, but with distinct punctures on the vertex. Thorax yellow, 
with the base broadly infuscate, on each side with a very deep impression or plica, at 
the base in the middle distinctly punctate, elsewhere almost impunctate. Elytra finely, 
moderately closely punctate, with a scanty and very fine but somewhat elongate pubes- 
cence, with very indistinct traces of a sutural stria, of a fuscous colour, with an indistinct 
angular pale mark extending from the shoulder inwards and backwards, and with a 
smaller mark near the apex; the basal plica deep, slightly longer than the thoracic 
stria. 
The species may be placed next to Hydroporus affinis, Say, from which it is readily 
distinguished by its broader form, distinct pubescence, and the more elongate plica on 
