184 THE CANADIAN ENTOMOLOGIST. 



b. Striae as wide or wider than the interstices. 



Sides of thorax sinuate (.15 in.) squajuifcr, Lee. 



Sides of thorax crenulate (.13 in.) excavatus, Lee. 



bb. Striae narrower than the interstices (.13 in.), .siibaipreus, Rand. 



OcHTHEBius, Leach. 



These are amaller insects than the preceding, though of much the 



same habits. In some parts of the Southwest they are so numerous that 



tliousands of specimens may be taken from a small pool by stirring up 



the borders. They are particularly partial (in my experience) to such 



small ponds as have been formed by the partial drying of a small stream 



fed by springs. Dr. Horn has found them most abundant in shallow 



lunning water, adhering to the under side of stones. All are rather 



flattened, somewhat roughly sculptured little beetles, some of which look 



like very small Helophori, while others remind us by their shape of 



Corticaria. The table is extracted almost entirely from that lately 



published by Dr. Horn in the Trans. Am. Ento. Soc. for 1890. 



A. Thorax abruptly sinuate from middle, or deeply notched near the 



hind angles. Transparent border broad. 



b. Thorax with well-marked discal fovete. 



Disk of thorax sparsely punctate (.06-. 08 in.), .discretus, Lee. 



Disk of thorax impunctate (.07 in.) nitidus, Lee. 



bb. Thorax without discal foveas, coarsely punctate 



(.oS in.) cribricollis, Lee. 



AA. Thorax gradually sinuately narrowed from apex to base, transparent 



border narrow. 



Discal impressions of thorax forming continuous line ; lateral fovese 



broad and moderately deep (.06 in.) sculptus, Lee. 



Discal impressions very vague, the posterior only distinct ; the 



lateral fovea3 in the form of indistinct sinuous impressions (.06- 



.08 in.) Holinbergi, Mann. 



Hydr/Ena, Kug. 



H. pensylvanica, Kies., is found under the same conditions as 



Helophoriis and Ochthebius. It is a small blackish insect (.075 in.), the 



feet, palpi and margin of thorax testaceous. Thorax sub-quadrate, 



densely punctured, impressed at sides, elytra sub-opaque, with rows of 



sub-quadrate punctures. 



Hydrophilus, Geoff. 

 Includes two very large black insects, the giants of the family as 

 represented in America. They separate thus : — 



