314 



BULLETIN OF THE BUREAU OF FISHERIES. 



Genus HYDROPHILUS DeGeer. 



Hydrophilus (DeGeer, 1774, p. 371). 

 Hydrocharis (Hope, 1838, p. 125). 



This is a genus of medium-sized beetles, in which the presternum, instead of 

 being grooved where it meets the anterior end of the sternal crest, is entire and is 

 raised into a sharp keel. These are very active beetles, swimming rapidly and 

 running about on land with great agility. The adults appear to feed entirely upon 

 slgsd; but the larvae are as voracious as those of Hydrous and Tropisternus, and 

 although they have never been observed attacking young fish they are amply 

 large enough to do so. It is hence deemed expedient to include here an abstract 

 of the excellent description given by Wickham (1895) of the only species found in 

 the Fairport fishponds. The adults of this species are well distributed among 

 the ponds, in at least two of which they are very abundant, but careful search 

 every year for the larvae and pupae has resulted negatively. 



Hydrophilus obtusatus Say. 



Hydrophilus obtusatus (Say, 1823, p. 201). 

 Hydrocharis obtusatus (Bowditch, 1884, p. 1). 

 Hydrocharis obtusatus (Wickham, 1895, p. 168). 



Hydrophilus obtusatus (Richmond, 1920, p. 31; pi. 1, figs. 1-2; pi. 6, figs. 1-10). 



Egg case. — The egg case of this species is similar to that of Hydrous, but is smaller and is nearly 

 always covered with a dead leaf or something of the sort. The case is white except the fag ^ and the 

 base of the cover, which are brown; it is 10 to 12 mm. long, 9 to 10 mm. wide, and 8 to 9 mm. high. The 

 fag is cylindrical and tapers to a sharp point; it is 7 to 10 mm. long and is enlarged at its base into a 

 plate 4 to 5 mm. high. About 40 eggs are deposited in each case, and they hatch in 6 or 7 days. 



Habits of the larva. — ^These larvae are very similar to those of Hydrous, both in structure and habits. 

 They swim in the same manner and come to the surface to breathe, supporting themselves upon the 

 surface film by means of their cerci. When young, they feed readily upon Cyclops and other Entomos- 

 traca, and when fully grown they eat tadpoles, insect larv£s, and the larvae of other beetles. According 

 to Bowditch (1884), they require 30 days to become fully matured, and then they pupate and remain in 

 the pupa state until the following spring. This statement was strongly questioned by Richmond (1920) 

 and seems equally impossible to the writer. If it were true the pupa would certainly be frozen 

 during the winter, and it is not the kind of a pupa to be capable of withstanding such an experience. 



Description of the larva. — Color of dorsal surface greenish, head and prothorax chestnut, ventral 

 surface lighter. Form elongate spindle-shaped, broadest at the middle of the abdomen. Length 

 26 to 28 mm. Width 5 to 6 mm. Head narrower than the prothorax, inclined obliquely upward, the 

 frontal margin lobed at the center, the ventral surface with four long mottled patches more than half 

 the entire length. Antennae three-jointed, basal joint very long and fringed with short setae along the 

 inner margin, second and third joints much shorter. Mandibles with two teeth on the inner margin, 

 the distal one much larger than the proximal. Maxillae with a long basal joint, a short second joint 

 armed at its inner distal corner with a short process, a third joint half as long as the second, and two 

 terminal joints each of which is about as long as the second joint. Labium large, the mentum irregularly 

 hexagonal, with a distinct tooth on either side near the apex; palps two-jointed, the second joint much 

 the longer; ligula more than twice as long as the basal segment of the palps and slightly tapered. Ab- 

 dominal segm-ents with two dorso-lateral rows of blunt spines on either side, and a row of lateral 

 filamentary appendages, each tipped with two setae, on the first seven segments. The eighth tergite 

 forms the superior valve of the stigmatic atrium and bears a large chitinized plate; its posterior margin 

 is divided into four lobes, each tipped with several setae. The first seven tergites each show a trans- 

 verse row of four tubercles and each tubercle is tipped with a seta. The lateral filamentary appendages 

 are longer than in Tropisternus or Hydrous but do not function as gills. 



See p. 332. 



