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, 0. W., and M. R. Campbell, " Relation of Biology to Physio- 

 graphy," p. 131. 



t Simpson, C. T., " Evidence of Unionidae," pp. 134135. 



M 2 



