1920] Richmond, Studies on the Biology of the Aquatic Hydrophilidce 39 



middle and then converge. They are slightly bifid and sharply pointed. On the 

 outer side of the distal third are two small spines. Abdominal spiracles (second 

 to sixth 1 large, uncovered and the area about them well chitinized. 



Tropisternus sublaevis LeConte 



A specimen of this species was examined at the National Museum. 

 It is very close to T. glaber. The proximal inner teeth of both mandibles 

 are more reduced and the basal ridge of left mandible is lacking. 



Hydrous Leach 



The above generic name will doubtless be confusing to many be- 

 cause our representatives have for so long a period been known under 

 the genus Hydrophilus. Here are included the largest beetles of the 

 family and, in Ithaca, only one species is to be found, namely, H. 

 triangularis. This is well known to collectors and because of its large 

 size ; measuring over thirty millimeters in length, can not be mistaken. 

 Its specific name is evidently due to the triangular spots of yellowish 

 brown hah- on the abdominal sternites. 



Adults have been collected during the warm spring and summer 

 months under electric lights, toward which they often fly in large num- 

 bers. One specimen was captured as late as November 1 under an arc 

 • light. The most rapid swimmers of the family are included in this 

 genus. It is clearly seen that their bodies are well adapted for gliding 

 through the water with the least possible resistance. 



European authors have paid a great deal of attention to H. ater- 

 rimus and H. piceus, especially the latter, not only to their life history 

 but also to their biology in its various phases. The earliest mention 

 of the larval and pupal stages was made by Frisch as far back as 

 1721 but his unique error of describing the larva upside down and there- 

 fore ascribing dorsal legs to it takes away part of its value. Miger and 

 Lyonet follow about a century later and both papers are worthy of com- 

 mendation. The life history of H. aterrimus given by Schiodte is pre- 

 sented in the usual careful way of the author. 



The most complete work on the only American species considered 

 is that of Dr. Robert Matheson of Cornell University, published in 

 1914. He has very carefully followed the entire life history of H. 

 triangularis through all its stages from the egg to adult. Garman's 

 paper in 1881 on the egg-case and larva was well written but did not 

 include the entire life history. It was supplemented by Riley's paper in 

 the same year. 



