1920] Richmond, Studies on the Biology of the Aquatic Hydrophilidoe 67 



Philydrus perplexus LeConte 

 Plate XIV, Figures 1 to 10 



Egg-case, without its ribbon, shaped very much like the terminal joint of one's 

 finger. The top of the case is slightly concave, while the under side conforms with 

 the object to which it is fastened. The case proper is 1.8 mm. high and 1.56 mm. 

 across the top, where the greatest width is found. The filament is broader than the 

 diameter of the cap and, although varying in the different cases, is usually about 3.6 

 mm. in length. The round cap, covering the top of the egg-case proper, is continuous 

 with the inner layer of the ribbon. 



Newly Hatched Larva. — Length, 2.52 mm.; width, 0.39 mm. Whitish, 

 except brownish chitinized portions; integument dotted with minute setae. 



Head quadrangular, elevated slightly; fronto-clypeal suture weakly indicated, 

 more prominent at the sides; frons somewhat campanulate; epicranial suture very 

 short; gula reduced and pentagonal, the antero-lateral sides about one-third the 

 postero-lateral in length; gular sutures prominent and confluent; two small, hori- 

 zontal, elongate cervical sclerites present. 



Labro-clypeus possesses at the extreme right a prominent acute tooth and a row 

 of five to six setae; the tooth on the right seems to vary quite a little, in some cases 

 being apparently single, in others double and in some tending to be tridentate. Just 

 below there appears to be a flap which is irregularly serrate, and has a fairly promi- 

 nent tooth 1 at the extreme left. Lateral expansions of epistoma prominent, unequal, 

 acute and slightly exceeding the labro-clypeus. Epipharynx spinous. 



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

 first five placed at regular intervals while the sixth is a little more distant with its 

 axis nearly horizontal. 



Antennae fairly short, not attaining the mandibles but exceeding the distal inner 

 tooth; first segment equal to the second in width and nearly the same length; second 

 segment not noticeably swollen in the middle and bearing a small, colorless, finger- 

 like antennal appendage, in addition to the sense-cones at the latter's base; third 

 segment nearly twice as long as the appendage of the second segment, which is three 

 times as long and wide as the former, and bearing at its extremity several sense- 

 cones and long setae. 



Mandibles asymmetrical, fairly prominent, sharply pointed at their tips and with 

 the inner surface of the anterior piece slightly serrate; the left mandible with a single 

 anterior tooth while the right one possesses two; both of the anterior teeth serrate on 

 their inner surface, those of the left often very indistinct; molar areas smooth. 



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

 toward the apex, longer than the palpifer and palpus together, its inner surface 

 provided with a row of five stout setae, and several slender setae near the externo-distal 

 angle; palpifer small, the length five-eighths the width, bearing a single stout, inner, 

 lateral seta near its base and a rudimentary lobe possessing apical setae; palpus borne 

 by the palpifer, three-segmented; its first segment equal to the rudimentary lobe of 

 ^he palpifer in length and a little more than one-half the second, while the third is not 



iThis tooth may be a part of the labrum proper but in most specimens seems to be in line with the 

 serrate flap. 



