1920] Richmond, Studies on the Biology of the Aquatic Hydro philidce 63 



very closely resemble those of Philydrus and are very voracious. They 

 do not hesitate to devour each other and apparently flourish on Cypri- 

 dopsis and Tubifex. 



Little attention has been paid to the growth of the larvae but on 

 August 31 of the same year several full-grown larvae were placed in the 

 terrarium. One of these formed a cell and transformed on September 4. 

 The cell was firmly made and was apparently larger than need be, mea- 

 suring 7.5 mm. long, 7 mm. wide, and 4.5 mm. high. 



Egg-case. — Nearly semicircular; follows the contour of the abdomen but 

 slightly exceeds it. It measures 2.16 mm. long and is 2.88 mm. wide at the anterior 

 margin. The two strands which attach the case to the inner margin of the posterior 

 femora are short and flared at the point of attachment. All the eggs are pointed 

 inwardly and their contour is visible through the silken case. The silk on the under 

 side of the case is more tightly woven than that on the dorsal side. 



Newly Hatched Larva. — Length, 2.28 mm.; width at the thorax, 0.342 mm. 

 Whitish, except the brownish chitinized areas; integument dotted with minute setae. 



Head quadrangular, slightly elevated; front o-cly peal suture weakly indicated 

 except at the sides; frons gradually constricted towards the middle, semicircular 

 behind; frontal sutures uniting to form a short epicranial suture; gula reduced, 

 pentagonal, somewhat semicircular behind; gular sutures prominent and confluent 

 for a long distance; two smajl, horizontal cervical sclerites present. 



Labro-elypeus asymmetrical, with six distinct teeth, all equidistant from each 

 other except the two on the left which are set slightly apart from the other four. 

 Six setae are present, one on each side of each tooth except between the fourth and 

 fifth from the right. Lateral expansions of the epistoma prominent, nearly similar and 

 with obtuse angles, but not exceeding the labro-clypeus. Epipharynx spinous. 



Ocular areas in groups of six and indistinct; arranged somewhat in a circle; 

 the front five placed at regular intervals, while the sixth is a little more distant with 

 its axis nearly horizontal. 



Antennae fairly short, not quite attaining the tip of the mandible nor distal end 

 of the stipes; first segment not quite as long as the second segment, slightly con- 

 stricted; second segment swollen, about the same width as the first and bearing at its 

 disto-external angle a slender, finger-like antennal appendage as well as a spine-like 

 seta; third segment small, less than one-fourth the length of the second but longer than 

 the antennal appendage and possessing two long slender setae and several shorter ones. 



Mandibles stout, nearly symmetrical, their tips sharply pointed and each with 

 two inner teeth, the proximal tooth being smaller than the distal one; the proximal 

 tooth of the left mandible smaller than that of the right; the anterior pieces and inner 

 teeth indistinctly toothed on their inner surfaces. Molar areas smooth and rounded. 



Maxillae with joint-like palpifer; stipes stout, swollen, not noticeably narrowed 

 towards the apex, about two-fifths longer than the palpus and palpifer together, its 

 inner surface with a row of five stout set.ee, and two slender setae near the externo- 

 distal angle; palpifer short, transverse, and bearing an inner rudimentary lobe, 

 - -ing two apical setae; palpus slightly tapering; the first segment shorter than 

 the palpifer and less than one-fourth as long as the second palpal segment ; the third 

 segment slightly shorter than the second and with distal sense-cones. 



