WATER BEETLES m RELATION TO PONDFISH CULTURE. 



321 



first strip where it joins the latter, but tapers toward the free end. The case thus has no cap and is 

 very strongly flattened, so much so in fact that the first one found was taken for a simple piece of ribbon, 

 but in pulling it from the leaf it was torn open and revealed the eggs inside. These eggs appeared 

 freshly laid and hatched in seven days after being taken into the laboratory. 



Habits of the larva. — The habits of these larvae are very similar to those of the preceding species. 

 They have the same method of locomotion by means of the prolegs and the end of the abdomen and 

 spend most of their time above the surface of the water. Apparently they never swim but crawl about 

 slowly over the vegetation and along the sides of the aquarium. They feed readily upon the chironomids 

 and entomostracans in the aquarium and do not show any tendency to fight mth one another. Those 

 under observation also ate a batch of snail 's eggs that happened to l^e upon the same leaf as their own 

 egg case. 



Description of the newly hatched larva. — Length 2.35 mm.; width through the metathorax 0.32 mm. 

 Color gray, the eyes black, the head and thorax dark brown. The general structure of the body is the same 

 as that of the preceding species, with the following differences. The antennae are shorter and much 

 stouter, but the armature is very similar. The mandibles are longer and more slender, with differences 

 in the teeth, which are shown in the figures. The maxillae are considerably stouter, and the stipes is 

 armed with four or five large and strong spines on the ventral surface near the inner margin. The 

 labium is also stouter, the palpiger bears five large setae; the basal joints of the palps almost fuse on the 

 mid line beneath the ligula, and each is armed with five setae on its dorsal surface. The head is much 

 wider than long and is covered with scattered setae on its dorsal surface. The labro-clypeus is also 

 more heavily armed with spines and setae. The large spines at the sides show up prominently in dorsal 

 view, and the whole dorsal surface is more or less corrugated. 



Enochrus perplexus (Leconte). 



PMlhydrus perplexus (Leconte, 1855, p 371). 



PMlydrus perplexus (Richmond, 1920, -p 67; pi 14, figs 1-10). 



Richmond (1920) succeeded in securing the complete life history of this species, which he presented 

 in the reference given above, together with excellent pictures of the larva in different stages of develop- 

 ment and of the egg case. He also gave a very short (three and a half lines) description of the newly 

 hatched larva of Enochrus (Philydrus) ochraceus (p. 70), with a figure of the egg case, and another brief 

 description of the newly hatched larva of Enochrus (Philydrus) hamiltoni (p. 71). 



Genus TROPISTERNUS Solier. 



Tropisternus (Solier, 1835, p. 308). 



^ ' This is a genus of medium-sized beetles of an oval or elliptical form, smooth and 

 shining black in color, with the dorsal surface strongly convex. They are by far the 

 most common beetles in the fishponds and are so abundant that they play an im- 

 portant part in the economy of fish culture. They are all of them excellent swimmers 

 and are agile upon land, walking and running well, but not jumping at all. They 

 feed largely upon Anabsena and Clathrocystis, which float upon the surface of most 

 of the ponds during the summer months. Neither the adults nor the larvae molest 

 young fish, while they thomselves furnish excellent fish food. 



Tropisternus lateralis (Fabricius). Figures 128-136, 139. 

 Hydrophilus lateralis (Fabricius, 1775, p. 228). 

 Tropisternus nimbatus (Say, 1825, p. 205). 

 Tropisternus lateralis (Blatchley, 1919, p. 318). 



The egg case and the eggs. — The female of this species attaches her silken egg case to some convenient 

 water plant, the stem or the leaf of grass growing in the water, the leaf of Convolvulus grown in from the 

 edge of the pond, or the stem of Sagittaria. Failing these, any other water plant may be chosen or the 

 case may be attached to floating debris. Often several cases will be found upon the same support, and 

 as many as 12 have been seen upon one grass leaf. The actual spinning of the case was witnessed several 

 times and may be described as follows: Taking a position back downward upon a floating support, or 

 head upward on an erect stem, the female holds herself in position with her front and middle legs. She 



