424 Wisconsin Academy of Sciences, Arts, and Letters. 
withstand the grinding wear of the rubble. But since it is the 
sole food supply of the phytophagous petrophils it is obvious 
that these will not be found where no suitable food supply exists. 
Thus the caddis-worms of the rocky shores are for the greater 
part absent, or at least much rarer among cobble-stones,—due 
primarily to the absence of their food-plant. 
In a measure, this absence of caddis-worms may be due also 
to the lack of sufficient protection; for while their cases are 
built strongly enough to withstand the impact of waves and 
spray, most of them would fare only indifferently well in the 
gravelly areas. As a matter of fact, the majority are absent, 
except Leptocerus ancylus, an occasional Leptocerus dilutus, and 
the Hydroptilids Agraylea, Ithytrichia, and Hydroptila, which 
live on Cladophora. But all of these are proportionately much 
less frequent, even among their food-plants, than in the rocky 
areas. The scantier representation of the may-flies,—that is, of 
Heptagenia, Ecdyurus, Baetisca, and Caenis, is probably due di¬ 
rectly to the undertow and its drift,—for these larvae have no 
further shelter beyond their chitinous covering. Hyalella, and 
the irregular component of beetles and Hemiptera are all more 
scattered. 
The characteristic of the cobble and gravel fauna is, there¬ 
fore, that its representation of clinging forms is much smaller 
than that of the rocky areas. On the other hand, the number 
of burrowing species is much greater. In fact, burrowers may 
be said to dominate,—for the moving sands and gravel are 
much more favorable to their existence in tubes and burrows 
than to the exposed dingers. Thus, Sparganophilus eiseni, 
the “blue earthworm,” is practically confined to the pebbly 
shores, while burrowers and tube-builders like Stenelmis, 
Gomphus fraternus. Ephemera varia, Argia putrida, Chirono- 
mus digitatus, C. lobiferus, C. modestus, C. plumosus, C. ten- 
tans, Cambarus propinquus, Erpobdella punctata, and Nephel- 
opsis obscura find the gravel shores apparently optimal,—for 
nearly all of these are much more frequent here than anywhere 
else in the lake. It is especially true of Chironomus digitatus, C. 
tentans var?, and C. plumosus, and of Stenelmis crenatus larvae, 
Sparganophilus eiseni, Cambarus propinquus, and Ephemera 
varia. Erpobdella punctata and Nephelopsis obscura, as on 
the rocky shore, here also burrow at the shore margin, some 
10-15 cm. below the surface, under flat stones. 
