Muttkowski—The Fauna of Lake Mendota. 
425 
0. Sandy Shores .—The transition from gravel shores to sandy 
shores is nearly imperceptible and is marked primarily by the 
gradual diminution in the number of larger pebbles and rocks. 
The absence of the latter means that no clinging surfaces what¬ 
soever are left,—hence also a total absence of any larger plants. 
Secondly, the sand as a substratum is still more influenced by 
molar agents, and forms an exceedingly insecure bottom,— 
in fact, it lacks permanence entirely. 
Hence the fauna must cope with, (a) a bottom which is only 
transient, (b) the absence of clinging surfaces, (c) a bottom 
which shifts with the slightest disturbance, and (d) a result¬ 
ant absence of plant food. 
Yet it is surprising that even here some species manage to 
maintain themselves. Thus, I have found Sparganophilus 
eiseni and a Lumbriculid burrowing in the sand; Chironomus 
digitatus, one of our commonest forms, appears to have a pre¬ 
dilection for sandy and gravelly bottoms, and builds its tubes 
copiously along the sandy shores; C. modestus, C. tentans var?, 
and C. fulviventris imitate C. digitatus in this respect. Hyalella 
azteca is quite frequent as a visitor; and the Johnny Darter, 
Boleosoma nigrum (Raflnesque), patrols the shore quite com¬ 
monly in search of food; Chironomus digitatus is often the sole 
element in this food. 
D. The Sandy Shoals .— Physiographically, they lie between 
the breaker line and the shore proper, and are therefore about 
a meter or less in depth. Their extent may be considerable, in 
places stretching out nearly 300 meters from the shore. Phy¬ 
sically, they are composed largely of fine sand, with a very 
scanty floral growth of Vallisneria, Chara, Najas, and Pota- 
mogeton. Physiologically, they are less exposed to molar 
agents, since the waves lose their main impact at the breaker 
line; as a result there is a fair growth of vegetation. Yet even 
with the loss of their main force, the waves are strong enough 
to prevent the growth of emergent plants, except in much se¬ 
cluded spots; and in these the waves promptly begin to erect 
a barrier in the form of a bar, thereby cutting off the foreign 
complex. 
Because of the presence of plants, the fauna of the shoals is 
in many respects like that of the vegetation zone proper be¬ 
yond the breaker line. No component characteristic of the 
shores is found in these shoals, except the Chironomid species 
