50 Bulletin American Museum of Natural History [Vol. XLII 



Prothorax rounded at the sides, about the same width- as the head; anterior and 

 posterior of pronotum non-chitinized; rest weakly chitinized except along the sagittal 

 line; prosternum weakly chitinized in front of the coxa?; mesothorax and metathorax 

 about equal to each other in size, shorter but slightly wider than the prothorax. 

 Sclerites are not discernible. The pleural lobes are each surmounted by a seta arising 

 from an elongate cylindrical structure (see figure 5, Plate X). A spiracle present in 

 each externo-frontal angle of the mesothorax. 



Legs long, about one-half again as long as the thorax is wide; coxae transverse; 

 femora and tibia? about the same length; tarsi well developed, claw-like, one-fourth 

 shorter than the tibia? and with two inner setae. The two anterior coxa? are closer 

 together than the four posterior coxa?, which are about the same distance apart. 



Abdomen with eight distinct segments, narrowed and slightly lengthened pos- 

 teriorly, flattened above and arched below. Thr first seven tergites similar; indis- 

 tinctly divided into two folds, while the intersegmental membrane has only one fold ; 

 each pleurite protrudes and bears a long, slender, tracheal gill, the length of these 

 seven pairs of gills increases posteriorly. The second scutal fold has a transverse row of 

 four seta?, each arising from an elongate cylindrical structure (similar to those on the 

 pleurites of the thorax). Another seta, with such a structure at its base, present on 

 the dorsal side of each gill and slightly removed from the base of the gill. Spiracles 

 are at tip of small tubercles. The sternites have similar folds but no tubercles are 

 discernible. Eighth segment short, cylindrical and with two small spiracles 1 on the 

 middle of its dorsal surface and a few posterior seta?. The anus terminates this seg- 

 ment. 



Full-grown Larva. — Length, 5.6 mm. (not counting the gills); width at the 

 second abdominal segment, 1.68 mm. Pale yellowish with chitinized areas yellowish 

 brown. Head, 0.576 mm. wide, 0.36 mm. along the mid-dorsal line. First antennal 

 segment much longer and about one-half again as long as the second segment. 

 The whole antenna more slender. Labium very indistinct. Body gradually widened 

 as far as the second abdominal segment and then narrowed. Segmentation is much 

 more pronounced as is the chitinization also. Mesothorax with two reduced sub- 

 triangular sclerites. Two small horizontal pro-mesotergal sclerites present. Meso- 

 thoracic spiracles distinct and meso- and metapleurites each with a prominent wart- 

 like tubercle corresponding in position to the gills of the segments. Pra?scuta of meta- 

 thorax and first four abdominal segments visible. Legs much shorter, not as long as 

 the thorax is wide. 



Peculiar structures noted at base of seta? on posterior fold of abdominal scuta 

 replaced by small but distinct, rounded tubercles. The gills are much shorter in 

 proportion to the body and possess no dorsal seta near their bases. 



Pupa. — The characters used by Schiodte in his pupal key are as follows: 

 "Motory styli of abdominal tergites in fours; abdominal tergites with a small 

 lateral tubercle on each side; spiracles not concealed; abdominal pleurites not 

 distinctly separated from the tergites; styli of pleurites very short and conical; 

 lateral styli of abdominal tergites very long and slender ; prothoracic styli long and 

 slender; cerci elongate, tapering, crooked and distally multiannulate." The figure 

 shows twenty-six pronotal seta? or two more than is characteristic of the Hydrobiina?. 



^The position of these spiracles recalls the position of those found in the pseudo-metapneustic 

 Hydrophilidae and probably indicates the degeneration of that type. 



