212 DIPTERA OF NORTH AMERICA. [PART II. 



Hydrophorus differs from Scellus by the fore femora and fore 

 tibise not being provided on the under side with long thorns, 

 catching between each other, by the tip of the fore tibiae not being 

 elongated into a clumsy -projection, by the middle tibise of the male 

 not being adorned with long hair, by the hypopygium not having 

 .those peculiar pale-colored appendages, which distinguish the 

 species of Scellus, &c. Liancalus has no notches on the third 

 joint of the antennae, its fore femora are not thickened and un- 

 armed, and it has bristles before the incisures of the abdomen, so 

 that no mistake can occur between the species of Hydrophorus 

 and Liancalus. 



The name of Hydrophorus (from i'Swp, water, and ^'petr, to 

 carry) has been bestowed upon these insects with reference to the 

 ability of many of the species to run even upon agitated waters. 



The species of Hydrophorus known to me are distributed over 

 Europe, Northern Asia, Africa and North America. There is no 

 perceptible habitual difference between the species from the dif- 

 ferent parts of the globe. 



Table for the determination of the Species. 



, ( Face with white dust, shining green above. 1 innotatus, nor. sp. 



I Face with brownish-yellow dust, opaque above. 2 



( Third and fourth longitudinal veins convergent. 2 pirata Lw. 



\ Third and fourth longitudinal veins parallel. 3 parvus Lw, 



Description of the Species. 



1. H. innotatus, nov. sp. $ and 9. Olivaceo-aeneus, scutello 

 virescente, abdomine viridi, femoribus tibiisque viridibus, tarsis nigris, 

 facie supra viridi-splendente, polline pleurariim albido, venis alarum 

 cinerascentium atr'is, longitudinalibus tertia et quarta apicem versus 

 paulo convergentibus. 



Metallic olive-brown with greenish scutellum and green abdomen ; femora 

 and tibise green ; tarsi black ; face shining green above ; pleurae with 

 whitish dust ; wings gray with black veins ; the third and fourth longi- 

 tudinal veins somewhat converging towards their end. Long. corp. 

 0.13. Long. al. 0.22. 



The dust upon the face is yellow-brownish immediately below 

 the antennae ; otherwise everywhere white in the male, but so thin 

 upon the entire upper part of the face that its metallic-green color 

 becomes distinctly perceptible ; in the female the face is covered 

 with white dust only along the sides, upon the middle with 



