WATER BEETLES IN RELATIO^T TO PONDFISH CULTURE. 



291 



triangular shield, clearly outlined by a very narrow yellow margin. The apex of the triangle is posterior 

 and the base anterior, each of the three sides are emarginate, and the anterior corners are broadly rounded. 

 From each side a broad ribbon of dark brown extends a short distance outwards and backwards, then 

 turns at a right angle forwards and outwards to the eyes (fig. 40, p. 288). The brown band along each 

 lateral margin behind the eyes is much wider than in the preceding larva, and there is often a large 

 brown spot on the base of each mandible. 



The labrum, with the peculiar fringe on its anterior margin, is relatively wider and fills nearly the 

 entire space between the bases of the mandibles. The sculpture on its surface is also radically different, 

 being made up of longitudinal instead of transverse lines. The maxilla differs as in Figure 45 (p. 288); 

 the labium is relatively longer and narrower ; in maculosus the palpiger is more than four times as wide 

 as long, but in the present species it is only a little more than twice as wide as long (fig. 47, p. 288). There 

 are other minor differences, but the present larva can be easily recognized by its darker color, by the 

 telescoping of the body segments, by the shortness of the first three abdominal segments, and by the 

 pattern of the dark figure in the center of the dorsal surface of the head. 



Description of the pupa. — This pupa is 4.5 mm. long and 2.5 mm. wide, light green in color, darker 

 on the dorsal surface and through the center of the body, with the posterior portion of the digestive 

 canal a dark brown, almost black; the wings, legs, and mouth parts are white, the eyes and posterior 

 cerci light brown. In comparison with the pupa of the preceding species the head is more quadrangular, 

 with a truncated anterior margin, slightly emarginate at the center. The femurs of the first legs extend 

 outward at right angles to the body axis, and the tarsi are turned backward parallel with the axis and 

 some distance apart. The tarsi of the second legs are crossed but reach back nearly to the posterior ends 

 of the wings. The tarsi of the third legs are also crossed and extend backward only to the sixth segment. 

 The eighth segment is much shorter than in maculosus and the cerci are narrower and straighter. 



Description of the adult. — Sharp (1882), in his excellent memoir of the Dytiscidse, said with reference 

 to this species: *'In the three individuals I have examined I can find no distinction from maculosus 

 except the darker color and more indistmct markings of the elytra, which, however, are so similar in 

 the two that I am inclined to think them one species." Blatchley (1910), however, in his Coleoptera 

 of Indiana, distinguished them as separate species, and an examination of the mouth parts confirms 

 his opinion. In the mandibles the terminal tooth of the present species is longer and more slender, 

 the secondary dorsal tooth is farther removed and its inner margin reaches nearer to the base of the 

 appendage, and the ciliated ridge does not reach the base. In the maxillae the palp is longer and more 

 slender; the rest of the appendage is much shorter and thicker. In the lower lip the mentum is much 

 longer and narrower and of an entirely different shape; the labial palps are longer, much thicker, and 

 more densely setose. These differences, combined with those found in the larva and pupa, fully waiTant 

 the separation of the species. This beetle is not quite as widely distributed as the preceding, but is 

 still common in most of the ponds. Both larvss and adults are so small that they can not harm young 

 fish but furnish excellent food. 



Genus THERMONECTES Crotch. 



Thermonectes (Crotch, 1873, p. 402). 



A genus of medium-sized, rather convex species, which are excellent swimmers 

 and agile jumpers. The head is dull yellow with the vertex and an M -shaped mark 

 black; the thorax is also yellow with two transverse black lines. In the males the 

 front tarsi are strongly dilated and bear two or three large basal sucking disks and 

 numerous smaller unequal ones. The hind tarsal claws are unequal. Neither the 

 larvae nor the adults ever menace young fish or display any tendency toward canni- 

 balism, but are exceptionally peaceable. 



Thermonectes basilaris (Harris). Figures 52, 54, 55, 57, 58, 60, 62, 64, 65, 67, 69, 70, 72, 73. 



Acilius basilaris (Harris, 1828, p. 8). 



Thermonectes basilaris (Sharp, 1882, p. 684; pi. 17, fig. 212). 



Eggs. — The eggs are laid singly below the surface of the water in the stems of crex grass, rushes, or 

 other water plants and hatch in four or five days. 



Habits of the larva. — Four of these larvae were captured August 6 and kept in an aquarium for a week, 

 when two of them died and the other "two pupated on being placed in artificial mud chambers. This 



