Sept., I9I7-] Fall: New Dytiscid^. 177 



recognized by the broader, simpler elytral markings, which leave on 

 either side of the sutural stripe an anterior suboblong pale space, 

 conspicuous in all examples before me, but which in allied species is 

 much narrowed or broken up by the dark markings. Mixtns is a 

 slightly larger species of a darker rufotestaceous color, the dark 

 areas of the elytra predominating (dark and pale areas about equal 

 in semiflaviis) , the form slightly different, the elytra being a trifle 

 more pointed behind, with the point of maximum width nearer the 

 base; the punctuation of the head finer and sparser, that of the elytra 

 a trifle sparser and coarser, and of the metasternum slightly sparser 

 than in semiftavus. Scriccus has the more nearly elliptical form of 

 semiflavus, and a similar though more pronounced golden pubescence ; 

 in size it is distinctly larger and the elytral markings are more nu- 

 merous and pronouncedly vittate in character ; the punctuation of the 

 metasternus and coxal plates is rather finer but denser than in semi- 

 flavus. In both mixtns and sericeus the anterior tarsal claws of the 

 male are nearly as in semiflavus. For comparison with the very 

 closely allied placatus, see the following: 



Hydroporus placatus new species. 



Very closely allied to the preceding species, between which and sericeus 

 it divides allegiance. Its size is scarcely as great as sericeus, but evidently 

 larger than semiflavus. Its markings are those of semiflavus except that there 

 is a tendency to suffusion on the elytra which diminishes the size of the ante- 

 rior subsutural pale area and in some examples more or less completely oblit- 

 erates the postmedian discal pale markings. The dark spot at the apical mar- 

 gin of the thorax is small, occupying about the middle third of the width as 

 in 'semiflavus ; it is much more extended in sericeus. The punctuation of the 

 elytra is evidently finer and denser than in semiflavus, and that of the under 

 surface is also denser, though scarcely appreciably finer than in the latter. In 

 sericeus the punctuation above is nearly as in placatus, while that below is 

 somewhat finer though about as dense. Length 3.9 to 4.3 mm. ; width 2 to 

 2.2 mm. 



Oregon (Corvallis), id* (type), 4 ?'s; my own collection. 



In the single male, the front claws are a little stouter and more 

 suddenly bent, and a little sinuate on their inner margins, the anterior 

 claw just perceptibly shorter. In semiflavus the front claws of the 

 male appear to be a little more unequal and scarcely at all sinuate. 

 In sericeus the inequality is a trifle more evident, the front claw not 

 sinuate, the rear one somewhat so. Possibly these differences would 

 not hold constant in a long series. 



