192 THE CANADIAN ENTOMOLOGIST. 



The present paper is intended for a supplement to those already pub- 

 hshed, while it is believed that in a few instances inaccuracies in them are 

 corrected, and some omissions are supplied ; yet it is acknowledged 

 that it is far less complete than it might have been, had full advantage 

 been taken of the material at hand. The dissected parts, particularly 

 those of the mouth organs, which served for the drawings of the figures, 

 have been mounted in balsam for preservation. 



The larva of Psephenus has been compared with those of HelicJms and 

 Elviis ; from the latter it is said to difier in no important particular. 

 Figure 2 of the plate represents a larva supposed to be that of Helichus 

 lithophiliis, Germ., and is introduced for the purpose of comparison with 

 Ps. Lecontei (Fig. i). The general resemblance is close, some essential 

 differences appear, but no full description of the larva of Helichus is at 

 hand for comparison. 



The young larva of Psephenus is found clinging to stones, the shells of 

 Uiiio, old wood and the like, usually where the flow of water is considerable, 

 often in the wild rapids, yet they have been taken in quiet water along the 

 shore, or even in ponds entirely cut off from flowing water ; their flat, 

 disc-like form, concave below, marginal cilia and powerful legs enabling 

 them to resist the swiftest current. 



Excluding the head the larva is made up of twelve rings ; the body 

 proper is but little broader, relatively, than that of many other Coleopter- 

 ous larv;^ ; the shield form is due to an uncommon extension of the tergal 

 folds, pleurites of the first ten body rings. The prothoracic segment is 

 broad, and extends over the head like a buckler ; it is divided by sutures 

 into six parts ; those on either side of the median suture are each divided 

 into two by a suture from near the anterior edge obliquely backwards to 

 near the middle of the posterior border ; the external pieces correspond 

 with the pleurites of the following rings (Fig. 1, a). The second and third 

 thoracic rings are broad, nearly equal, the expanded plate of the meso- 

 thorax is, however, more wedge-shaped than that of the post-thorax, in 

 order that its outer margin may complete the outline curve with the pro- 

 thorax. The first three rings occupy one half of the expanded surface of 

 the larva. 



The seven succeeding abdominal rings have nearly equal length, but 

 gradually diminish in width from the first, the widest part of the body, to 

 the eighth and ninth. These two have nearly equal width. They are, 

 however, considerably longer than the abdominal joints above them. The 



