204 
IOWA ACADEMY OF SCIENCE 
It will be apparent from the table that there are exceptions to the 
above mentioned rule of distribution, as the aquatic Chrysemys cinerea 
hellii occurs principally to the west of the eastern forest region, Miile 
Liopeltis vernalis is an open habitat form and occurs both in the eastern 
forest and prairie-plains regions. These cases are exceptions, however, 
and do not disprove the general statement. It will also be noted that 
unlike the ornis there are few decidedly eastern forms in the fauna. I 
believe that this is due largely to the lack of collections from this habitat, 
and that when the fauna of the region is more perfectly known more 
eastern forms will be found in the region and associated with the mar- 
ginal forest habitats. 
However this m^ay be, the table shows that, as far as our present knowl- 
edge goes, the reptile-amphibian fauna of northwestern Iowa is composed 
chiefly of a mixture of those forms ihat are either of western distribution 
or occur both in the plains and eastern forest regions and that the ma- 
jority of the prairie types are western, and the forms closely associated 
with the acpiatic conditions of wide ranging, distribution. This is not 
other than should be expected for: 
1. The habitat conditions in the marginal forest along the streams 
and lakes most closely resemble those of the eastern forest region, as 
shown by the fact that the habitats are occupied by plants from the 
eastern forest. 
2. The aquatic and shore habitats of the prairie-plains region are in 
direct communication with the eastern forest region by means of the 
tributaries of the Mississippi and Missouri rivers. 
3. The prairie (especially the upland) habitats most nearly approach 
the general conditions on the Great Plains, into which they merge to the 
westward. 
Referring to plants, Harvey'” has recently stated similar conclusions as 
follows : 
A study of the floristics shows indisputably the commingling of forms of 
diverse geographical affinity. An unmistakable floristic relation, in many cases 
specific, exists with a southwestern and southeastern center of post-glacial 
dispersal. To the east and southeast the deciduous forest type becomes increas- 
ingly characteristic, while to the west and southwest the plain or prairie type 
gradually predominates; the region thus lies in the western border of the 
tension zone in which migration from these two competing centers of distribu- 
tion meet. Prom the southeast the dispersal route has been up the Missouri 
valley; while the northwestern migration has spread diagonally across natural 
drainage lines, following the upland plains. 
iojCoc. cit., p. 85. The reader is referred to Harvey’s paper for a detailed discussion 
of the factors involved in the distribution of the flora in this region. 
