growth of grasses and some shade provided by
the small leaves of the thorny trees.

In Michoacan the rainfall is heaviest on the southern slopes of the
Sierra de Coalcoman and somewhat less so on the southwestern slopes of
the Cordillera Volcanica. At these relatively low elevations (150 to 600
meters) there is tropical semi-deciduous forest, characterized by
relatively dense shade throughout the year and by a leaf mulch on the
ground. This type of forest forms the gallery forest along the larger
streams in the Balsas-Tepalcatepec Basin and on the Pacific Coastal
Plain.

Rainfall also is heavy on the high mountain ridges, where temperatures
are low. On these ridges, fir forest, often mixed with pine and oaks, is
found. This habitat is characterized by a cool, moist climate, many
rotting logs, and a moist ground cover of leaves and needles.

Most of the mountains are covered with pine-oak forest, which in most
places is decidedly subhumid, but where this forest occurs on the
windward sides of high ridges, it sometimes is noticeably humid. In
this forest the important animal habitats include the needle- and
leaf-litter, and in some areas, bromeliads.

The rolling terrain of the Mexican Plateau supports cacti, small
leguminous trees, and grasses. Like the arid tropical scrub forest, this
type of vegetation, the Mesquite-grassland association, is deciduous and
thus provides little shelter in the dry season. Unlike the areas in
which arid tropical scrub forest is developed, the Mesquite-grassland is
found in areas having warm days and cool nights.

GEOGRAPHY OF THE HERPETOFAUNA

Although the main part of my final report on the herpetofauna of
Michoacan will deal with the geographical and ecological patterns of
distribution of the herpetofauna, a brief summary of the faunal
assemblages is presented here.

In Michoacan there are two major faunal assemblages, one in the
lowlands, and one in the highlands. A large number of the species
inhabiting the lowlands are wide-ranging species, such as _Bufo
marinus_, _Iguana iguana_, and _Boa constrictor_. Sixty-three species
are known to occur on the Pacific Coastal Plain; 41 of these, together
with 36 others occur in the Balsas-Tepalcatepec Basin, a physiographic
region to which several species of reptiles are endemic; for example,
_Enyaliosaurus clarki_, _Urosaurus gadowi_, _Cnemidophorus calidipes_,
and _Eumeces altamirani_.

Generally speaking, the members of the