BONY-PIKE AND BOW-FIN 
163 
upon physiographic evidence—such as the character of the 
Tennessee-Coosa divide, the nearness of the gorge below 
Chattanooga, and the general arrangement of the drainage 
lines.* Now it is a remarkable fact that Dr. Simpson has quite 
independently come to a similar conclusion from a study of 
the fresh-water mussels. The upper Tennessee and also the 
Alabama River abound in species of the genus Pleurobema, 
which is quite absent in the lower Mississippi. The species, 
moreover, found in these two rivers are very closely allied, so 
that this and other characters led Dr. Simpsonf to the con¬ 
viction that- at some time in the middle or later Tertiary, the 
Tennessee River must have flowed southward into some of 
the streams of the Alabama drainage, discharging its waters 
in this manner direct into the Gulf of Mexico:. 
In the fourth chapter (p. 88) I cited some ganoid fishes 
of the Mississippi in illustration of the zoological relation¬ 
ship existing between eastern North America and eastern 
Asia. Two other well-known and very remarkable ganoid 
fishes live in the Mississippi basin, viz. the bow-fin (Amia 
calva) and the bony-pike (Lepidosteus osseus). The former 
is the sole surviving member of the family Amiidae. Long 
ago, in early Tertiary times, the genus Amia inhabited middle 
and western Europe, while it is amply represented in the 
Eocene (Bridger) deposits of Wyoming. Bony-pikes lived in 
Europe from Eocene to Miocene times. In America they 
likewise appeared in the Eocene period, and persisted until 
the present day. It is evident that both the bow-fin and bony- 
pike are extremely ancient types, which have managed to 
survive a great many geological changes of the American 
continent. Their ancestors must have travelled to Europe 
in the dawn of the Tertiary Era, assuming of course that 
North America was the birthplace of these genera. Did 
they travel from river to river and from lake to lake across 
North America and Asia to Europe, or did they utilise the 
fresh-water streams of a shorter direct land bridge to 
Europe ? These are problems to be solved. The zoological 
* Hayes, C. W., and M. R. Campbell, “ Relation of Biology to Physio¬ 
graphy,” p. 131. 
t Simpson, C. T., “ Evidence of Unionidae,” pp. 134—135. 
M 2 
