MuttUowski—The Fauna of Lake Mendota. 
379 
proximately identical. Comparably, the aphytal area, and the 
zone of decomposition are identical. 
The littoral area in Lake Mendota extends to a depth of 
about 7 meters. Usually, the littoral area is accepted as the 
region of plant growth. In the present paper, the littoral area 
is regarded as composed of two major divisions, the eulittoral 
and sublittoral. The eulittoral area is the region of photo¬ 
synthesis,—hence the region of plant growth. Below this lies 
a region of variable extent, a region of heaping refuse, a place 
where a minimal amount of photosynthesis may take place, 
but which is characterized by the absence of spermatophytes 
among plants; this is the sublittoral area. Parallel to the 
nomenclature of pelagic waters into euphotal, dysphotal, and 
aphotal regions, these two divisions may be termed euphytal, 
and dysphytal. 
In Lake Mendota the eulittoral area extends only to a depth 
of 5 or 6 meters. This is rather surprising in comparison with 
some other lakes, such as the alpine lakes of Europe, where 
vegetation may extend to a depth of 25 and more meters. 
Lake Mendota presents the conservative extreme in this re¬ 
spect. As an example of the other extreme, Ekman (1915) 
reports green Characeae from a depth of 50 and more meters 
in Lake Vaettern, in Sweden, hence from a depth greater than 
twice the maximum depth of Lake Mendota. • 
The eulittoral area has three well-defined regions, or zones: 
shore line, rachion (breaker line), and plant zone. 
Bachion (Breaker Line). —The rachion marks the point 
where the interaction of waves and returning undertow is 
greatest. In Lake Mendota this is at a depth of about 1 me¬ 
ter. The rachion may be continuous with the shore line (on 
steep grades) or entirely disconnected (shoals). In the latter 
places it is frequently divided into an inner” and “outer” 
bar, a few meters apart from each other, and often many me¬ 
ters distant from the shore proper. In its physical aspects the 
rachion resembles the stony and gravel shores. 
Shore Line. —The shore proper offers three varieties of habi¬ 
tats: (a) the rock beaches, characterized by shattered rocks 
and large boulders, which are not easily dislodged by waves; 
(b) the gravel (stony) beaches, composed of pebbles and 
stones, with an admixture of sand, the latter having the effect 
of smoothing the available surfaces; and (c) sand beaches. 
