60 Bulletin American Museum of Natural History [Vol. XLII 



near its base, and an inner rudimentary lobe, possessing apical seta?; first segment of 

 palpus the same length as the rudimentary lobe of the palpifer and a little more than 

 half the second, while the third is not quite as long as the first two together but more 

 slender and more cylindrical; each bears a few slender setae, the terminal segment 

 possessing a group of sense-cones at its extremity. Articulating maxillary piece well 

 developed. 



Labium extending forward almost as far as the tips of the mandibles; submentum 

 very small; mentum somewhat cordiform; palpiger dome-shaped, four-fifths the 

 mentum in length, bearing several prominent setae clorsally; labial palpus with first 

 segment short, second segment about three times as long and bearing sense-cones at 

 its tip ; ligula present and slightly exceeding the first segment of palpus in length. 



Prothorax with sides slight^ rounded, of same width as head. Anterior third of 

 pronotum non-chitinized, sagittal line present, prosternum with two fairly large 

 sclerites in front of the coxa?. Meso- and metathorax a little narrower and shorter 

 than the prothorax; sclerites of mesonotum and metanotum fairly large, the former 

 subtriangular and the latter elongate; two elongate sclerites are present in the pro- 

 mesotergal conjunctivum; sagittal line prominent. A spiracle on a small tubercle at 

 each antero-lateral angle of the mesothorax. 



Legs fairly long, slightly longer than thorax is wide; coxae transverse, grooved 

 laterally to receive the femora; femora longer than the tibiae; tarsi well developed, 

 claw-like, about as long as the tibiae and bearing two inner seta?. The anterior coxae 

 are closer together than the four posterior coxae, which are about the same distance 

 apart. 



Abdomen with eight prominent segments and very slightly narrowed caudally, 

 ninth and tenth rudimentary. The first seven tergites similar and separated by a 

 conspicuous intersegmental membrane; each of the former has three transverse folds 

 while the latter has only one. The first tergite bears two transverse chitinized patches 

 on its prsescutum. Lateral tubercles are not clearly defined but there are apparently 

 two larger ones on the segment and two smaller more pointed ones on the membrane 

 following. The sternites are not chitinous and have folds corresponding to those of 

 the tergites. The eighth tergite represents the superior valve of the stigmatic atrium 

 and bears a large chitinous plate, which is a little broader than long. The caudal 

 border of the superior valve is chitinized, bears a few seta?, and is slightly bilobed. 1 

 Procercus one-segmented, subcorneal, with a chitinous plate on the inside and a group 

 of three seta? arising dorsaliy from tubercles on their apical half. Mesocercus two- 

 segmented and chitinous; the first segment dome-shaped, bearing a central dorsal 

 seta as well as a ventral seta; the second segment very small, papilliform and bearing 

 a terminal seta (0.4 mm. long); between these two segments there are several sense- 

 cones in the membrane. The ventral valve, or ninth tergite, is trilobed posteriorly 

 and the lateral lobes possess chitinous areas from which arise two seta? mounted on 

 tubercles. The acrocerci 2 are evidently attached to the under side of these lobes and 

 each bears a terminal seta. The median lobe is large and somewhat cordiform; its 

 dorsal surface covered, except for a narrow border, with a chitinous plate. Near the 

 caudal margin are four seta?, the outer two of which are in line with each other and a 

 little anterior the median two. 



^he outer lobes, which are present in many of the Hydrobiina>, are indistinct here. 



2 A question arises as to whether the acrocerci are the dorsal tubercles and setae or the ventral. It is 

 difficult to determine; but. from position as described by d'Orchymont, I have considered them as 

 ventral. 



