416 Wisconsin Academy of Sciences, Arts, and Letters. 
The larvae are water-breathers, extruding an anal tracheal 
tuft for the purpose. In general they live in tiny burrows 
made in gravel or in sand between stones, but they may fre¬ 
quently be found crawling freely over rocks in depths from 
the shore-line to 6 meters. Besides crawling, the larvae have 
a quite unusual method of swimming; this is retro-progressive 
(i. e., moving backward), but in an inverted position, the re¬ 
curved caudal segments flapping violently. For pupation the 
larvae leave the water and in the moist sand make a pea¬ 
shaped burrow in which they transform. Pupation begins in 
the middle of August and lasts for about 10 days. The adults 
immediately reenter the water, where they copulate and de¬ 
posit their eggs on rocks. 
In a sense, the adults are true water-breathers. For they 
remain submerged continually, rarely, if ever, coming to the 
surface for the replenishment of their oxygen supply. Brocher 
(1912) in a very interesting paper has shown that Stenelmis 
adults exchange oxygen very readily through the abdominal 
plastron of air. i 
In Lake Mendota Stenelmis adults occur chiefly in plant 
marl, gravel, and sandy bottoms in depths up to 10 meters. 
I have not found a single larva nor adult in any of the eight 
hundred or more shore fishes examined. 
Dry ops lithophilus Germar; Parnid sp. larva. 
I do not know the larva of Dryops lithophilus, but suspect 
that it is the Elmis-like, or “ trilobitic ’ ’ larva found fairly 
abundantly on rocky shores, and here referred to as Parnid sp. 
I have failed to breed this larva hitherto although I assembled 
them in considerable quantities. The optimal habitat of the 
larva is between one-half and one meter depth on rocky shores, 
apparently where wave action is quite strong. It also occurs 
among the rocks of the Yahara spillway. 
Dryops lithophilus frequents the moist places of the shore 
and may occasionally descend into the water. 
Psephenus lecontei Leconte. 
The characteristic larva of this species is the famous ‘Gvater- 
penny” or ‘‘stone-penny”* of the rocky shore. The larvae oc¬ 
cur in depths of 0-6 m. and seem to be restricted to a rocky 
and stony habitat. They are always found on the under-side 
