Muttkowski—The Fauna of Lake Mendota. 
419 
DEPTH DISTRIBUTION. 
Table 7 (p. 477) indicates the distribution of the species of 
the various groups in the order of their depth occurrence. The 
optimum depth has been noted in italics. Distinction 
should be made for species whose depth distribution extends 
below 7 meters. In many of these it means that they extend 
over the entire lake bottom beyond the depth of 7 meters; for 
others the distribution may be limited according to certain bot¬ 
tom conditions, and, more especially, by the gas content of the 
hypolimnion. 
ECOLOGICAL DISTRIBUTION. 
In its larger aspects the lake is divided into two areas, the 
littoral, and the aphytal area. The littoral area is assumed to 
extend from the shore margin to the lower limit of photosyn¬ 
thesis,—hence of plant growth. Below this is a region of com¬ 
parative quiet, of relatively mild changes, of no plant growth— 
the aphytal region. 
The littoral area permits of two subdivisions,—a eulittoral 
region, reaching from the shore margin to the lower limit of 
photosynthesis,—in Lake Mendota nearly synonymous with the 
limit of wave action; and a sublittoral region, a region of heap¬ 
ing of refuse and drift, lying next to the vegetation area, and 
synonymous in Lake Mendota with the lower limit of wave 
action. 
In the following the ecological habitats of these areas are taken 
up in both their vertical and horizontal aspects. The littoral 
area in vertical section can be regarded as composed of (I) The 
shore line, (2) the breaker line, and (3) the plant zone,—com¬ 
prising the eulittoral area; and (4) the shell zone—comprising 
the sublittoral area. ' 
The Eulittoral (Euphytal) Area. 
I. The Shore Line. 
The physical characteristics of the shore line vary somewhat 
in the different parts of the lake. In this paper the shore line is 
distinguished as that narrow strip of lake border which owing 
to the exposure to molar agents has a ‘‘clean-washed” appear- 
