THE CANADIAN ENTOMOLOGIST. 137 



that this guard is of prominent advantage for the plant. The enormous 

 numbers of the spores of the rust-fungus will scarcely be diminished by 

 these larvae to any extent, that the guard may be considered to be a prac- 

 tical advantage for the plant. 



The second point of interest in Mr. Trelease's paper is that the larvae 

 open the way for the fungus in the plants. I may state as an analogous 

 fact, that here the pustulae and pocks on the leaves of Pomaceae, made by 

 Phytoptus, are not rarely filled by fmigi, especially by the carbonized 

 ones. The last plant I received by the late Alex. Braun, in 1877, from 

 Blankenburg, Hartz., was a leaf of Sorbus aticuparia, with fungus immi- 

 grated in the galls of the mites. 



A NOTE ON SOME HYDROPHILID^. 



BY GEORGE H. HORN, M. D. 



Hydrophilus, as heretofore recognized in our fauna, contains two sets 

 of species, the one series large, the other relatively small. They also 

 differ in the form of the maxillary palpi and should properly be considered 

 distinct genera defined as follows : — 



Hydrophilus. — Terminal joint of maxillary palpi much shorter than 

 the penultimate, the second joint long, arcuate. Claws toothed. 



Tropisternus. — Terminal joint as long or even longer than the penul- 

 timate, the second joint moderately long and straight. Claws not toothed. 



The large species belong to the first series, and but two have appeared 

 in our lists. 



In the Biologia Cent. Am., vol. i, pt. 2, p. 54, Dr. Sharp mentions 

 two others as occurring in our faunal limits, H. ijisularis Cast, and H. 

 ater Fab. The former has long been known to us, but has remained 

 without name in our cabinets. The latter, which I have never seen, is 

 quoted rather indefinitely by Dr. Sharp, " Philadelphia, Texas." 



The species known in American collections are as follows : — 



IT. ovatus G. & H. (ovalis || Zieg.) Form more broadly oval, thorax 

 more deflexed in front. Prosternal groove open in front. Abdomen 

 opaque, densely finely pubescent, except a narrow space at the middle of 

 the last three ventral segments. 



