316 



BULUETIN OF THE BUREAU OF FISHERIES. 



retracted under the prothorax as far as the ocular areas. Thorax a little wider than the head; abdomen 

 a little wider than the thorax, the first seven segments about the same width with scalloped margins, 

 the eighth segment narrower, as wide as long, with a large dorsal sclerite, the ninth and tenth segments 

 rudimentary; there are no cerci except the minute ones connected with the atrium. 



Antennae short and three- jointed, the second joint the same width as the first and much longer, 

 with a long finger process at the outer distal corner; terminal segment not much larger than this finger 

 process, tipped with three long setae and several sense cones. Mandibles asymmetrical, curved, and 

 acuminate, the right one with three inner teeth decreasing in size proximally, the left one with two 

 toothed areas, each pectinated dorsally. Maxillae five-jointed, the basal joint (stipes) swollen and longer 

 than the rest of the appendage, its inner margin with five stout setae, the second joint (palpifer) a little 

 wider than long with a short finger process on its inner margin. Labium small, palpiger widened distelly, 

 palps two-jointed, the terminal joint four times the length of the basal and tipped with many sense cones. 

 Ocular areas outside the bases of the antennae; eyes in two nearly parallel rows. Color dirty- white to 

 grayish-brown. 



Pupation. — Richmond (1920) reported that of two larvae placed in a terrarium one pupated on the 

 surface of the earth and the other burrowed just beneath the surface. All the pupae found by the 

 writer were beneath the surface and 2 to 3 feet from the water's edge. This larva seems to select drier 

 mud than some of the others, and its pupal chamber is about 4 mm. in diameter, slightly longer than 

 wide. When the chamber is completed, the larva transforms almost at once and remains in the pupa 

 stage four or five days. 



Description of the pupa. — The most striking characters of this pupa are its exceptional width and the 

 great length of all three pairs of legs. It is 3.70 mm. in length, including the cerci, and has a width of 

 2.25 mm. through the thorax. It thus has the shape of a short and very wide spindle, which is sharply 

 tapered both anteriorly and posteriorly. When first formed it is bright sea-green in color, but soon 

 becomes white with black eyes. As development proceeds the legs, wings, and elytra become tinged with 

 brown. 



There are two styli above each eye, situated about half way between the eye and the mid line. The 

 anterior and posterior margins of the pronotum each carry 10 styli, and there is a transverse row of 4 

 across the center of the segment. The meso and meta notum each have two styli, and there is a transverse 

 row of 4 across each of the first 7 abdominal segments, the lateral one on either side mounted on a small 

 tubercle. The eighth segment has two small dorsal processes close to the mid line, and the ninth 

 segment ends in two cerci armed with long moniliform spines. 



The antennae are carried outward nearly at right angles to the body axis; the femora of all three 

 pairs of legs also extend in the same direction, while the tibiae and tarsi are curved inward to the mid line. 

 The tarsi are all tipped with spines; the first pair reach the first abdominal segment, the second pair 

 reach the center of the seventh abdominal segment, and the third pair extend well beyond the body to 

 the center of the cereal spines. The spurs at the tips of the tibiae on the hind legs are fairly prominent 

 but are concealed by the tarsi of the second legs. 



Description of the adult. — General form short and stout, nearly as wide as long and strongly convex. 

 Length 2 to 3 mm. Head and prothorax blackish-iridescent with a broad yellow margin on the thorax. 

 Elytra pale with dark striae; undersurface black, legs and palpi pale. Head covered with fine wrinkles, 

 the margin in front of the eyes yellow ; thorax three times as wide as long, as wide at the base as the elytra 

 and sparsely covered with fine punctures. On the elytra the punctures are very small and are set close 

 together in distinct and regular rows. 



Genus ENOCHRUS Thomson. 



Enochrus (Thomson, 1859, p. 18). 

 Philydrus (Solier, 1835, p. 315). 



This is a genus of small beetles, oval or elliptical in outline, blackish or brownish- 

 yellow in color, and covered with fine punctures regularly arranged. Each elytron 

 has also four rows of coarser punctures. These beetles are not as agile as Laccobius 

 and do not hide as persistently, but they swim fairly well and can run quite fast. 

 They frequent the smaller ponds and are found either at the water's edge or close 



