318 



BULUETIN OF THE BUREAU OF FISHERIES. 



to it in the Spirogyra and Mougeotia. Apparently they feed entirely upon these 

 algae. They are not abundant anywhere in the Fairport fishponds, but both the 

 adults and the larvae make excellent fish food. 



Enochrus nebulosus (Say). Figures 112-116, 118, 120, 122, 126, 127. 

 HydroUus nebulosus (Say, 1825, Supplement vol. 2, p. 277). 

 PMlydrus nebulosus (Richmond, 1920, p. 69, pi. 1, fig. 9). 



Egg case. — ^The egg case of this species is 3 mm. long, 2.50 mm. wide, and 2 mm. high at the center 

 of the cap end. The side next to the support is flattened and fastened rather securely. The cap is semi- 

 circular and slightly concave, the hinge margin straight, the free edge evenly rounded. The fag ^ is in the 

 form of a flat ribbon, a little narrower than the case itself, and uneven in width, but in general tapering 

 toward the free end. It is 8 to 12 mm. long and 1 to 1.70 mm. wide and is fastened to the support so that 

 it does not float in the water. Eight cases were found in pond 13B upon the undersurface of the 

 leaves of Potamogeton illinoensis. Each contained from 12 to 20 eggs, and they all hatched together six 

 days after being brought into the laboratory. Compare with this Richmond 's record (1920, p. 66) : 



Ten egg cases were made by a single specimen of PMlydrus nebulosus during February (indoors) and some of them were 

 placed below the surface of the water. The time required for hatching is from six to nine days. 



The eggs are regular ellipsoids 0.56 mm. long and 0.25 mm. wide, with a small triangular projection 

 at the end which is fastened to the wall of the case. 



Habits of the larva. — These larvse are very sluggish and crawl about slowly over the vegetation or on 

 the bottom close to the water's edge. They burrow in the mud or even crawl out of the water and may 

 be found under stones or debris close to the water, where it is always moist. When kept in a glass dish 

 indoors, they crawl up the sides of the dish above the surface of the water but never far enough to become 

 dry. In walking they use the large tubercles on the ventral surface of the abdomen just as a caterpillar 

 uses its prolegs, and the end of the abdomen functions like the posterior prolegs of the caterpillar. As 

 Richmond has stated (1920) the true legs move first, then the prolegs, and finally the end of the abdomen, 

 the whole motion being rhythmic. On a leaf or on the side of a glass dish they frequently cling to the 

 surface with their prolegs and the end of the abdomen and raise the head and thorax into the air, reaching 

 about in different directions. They can also move backwards in the same manner as the Tropisternus 

 larva, but with much less speed and agility. They can not, or at least they do not, swim. When thrown 

 into the water they immediately rise to the surface in consequence of the large amount of air in their 

 tracheae. They then float about with the posterior end of the abdomen above the surface film until they 

 strike some object upon which they can crawl. 



They showed no tendency to eat others of their own kind, as is the custom with most of the hydro- 

 philid larvae, but fed upon the minute Entomostraca, Bryozoans, etc., in the aquarium. A Potamogeton 

 leaf with egg cases attached was floated upon the water, and the larvse after emerging browsed around 

 upon this leaf and apparently found enough to eat. 



Description of the newly hatched larva. — Length, including the maxillae, 2 mm. ; width through the 

 metathorax 0.35 mm. Color gray with black eyes and the chitinized portions of the body and append- 

 ages brown. General form elongate but rather thickset, the abdomen not much narrowed posteriorly 

 and rather bluntly rounded. Head quadrangular, wider than long, slightly elevated, with almost 

 straight sides. Frontal margin sinuate; frons elongate, campanulate, reaching the entire length of the 

 head and practically obliterating the epicranial suture. Eyes fairly close to the bases of the antennae, 

 all six visible in dorsal view, the first (anterior) one enlarged, the sixth reduced in size, removed from 

 the others, and twisted so that its axis is nearly horizontal. 



The antennae are short, the tip of the second joint not quite reaching the palpiger of the maxillae, 

 the two basal joints of the same width, the first one a third shorter than the second, the third a fourth 

 of the length and a third of the width of the second. The second joint bears on its inner margin, a little 

 distal to the center, a sense cone tipped with a seta, and a long seta ventral to the base of the cone. On 

 its outer margin at the distal end, on a level with the base of the third joint, is a finger process, nearly 

 as long as the third joint, and outside of its base two sense cones. The third joint is tipped with several 

 long sense cones and a few setae. 



See p. 332. 



