422 Wisconsin Academy of Sciences, Arts, and Letters. 
ence of free-swimming Ceratopogoninae larvae of Palpomyia 
longipennis, and especially of Probezzia glaber and P. pallida. 
Yet except for Ithytrichia clavata none of these forms is truly 
petrophilous; they are to be regarded as primarily algophil, 
since they are found on filamentous algae in the lake wherever 
these occur. In the shore area they may occur on the under as 
well as the upper side of rocks and stones. 
Some burrowers are frequently found on the rocky shores. 
These are Stenelmis crenatus larvae and the older larvae of 
Ephemera varia. Here also may be found Cambarus propin- 
quus, which wedges itself under stones and heaps gravel about 
itself. All three are more common on gravel shores. 
Among vertebrates Cottus and Etheostoma fiabellare are char¬ 
acteristic of the rock beaches. These and the Crustaceans Hya- 
lella, Dikerogammarus, and Gammarus can be called migrants or 
visitors, for most of them migrate in unfavorable weather. Other 
visitors are the Hemiptera and adult Coleoptera. These very 
readily climb the rocks and leave the water during unpropi- 
tious conditions. 
A secondary zonation is indicated. While most of the species 
on the list are primarily petrophilous, they seem to prefer cer¬ 
tain regions of the shore. Thus, at the immediate shore margin 
one may invariably find hundreds of leeches that have burrowed 
under the rocks at a depth of about 10-15 cm. below the surface. 
Most of the petrophilous fauna prefers the middle ground be¬ 
tween the shore margin and the lower edge which marks the 
breaker line. This is illustrated in the case of Psephenus 
lecontei and its relative, Parnid sp.; Psephenus prefers the up¬ 
per middle ground, while the Parnid may be found more abund- 
anly toward the breaker line. 
Owing to the peculiar conditions of this shore area, and es¬ 
pecially because of the lack of vegetation except Cladophora, the 
food conditions are necessarily somewhat uniform. Alimenta¬ 
tion is possible only during relatively short periods. Since even 
then many of the forms do not wish to leave their shelter under 
the rocks, they must feed on the micro-organisms found in their 
immediate vicinity. This means a mixed diet. Several species, 
however, such as Polycentropus sp., Hyalella, and the Epheme- 
rid larvae, quickly mount to the upper side and feed on the 
Cladophora or on the very almndant microfauna and flora which 
breeds among the algal filaments. 
