276 Isthmus Barriers Separating Fish Faunas 



has been similarly elevated during the recent epoch. ... It 

 may be true, therefore, that the submergence of this isthmus 

 was one of the causes of the Glacial period, the continuation of 

 the equatorial oceanic currents westward into the Pacific having 



Fig. ISO.— Cauhphryne jordani Goode and Bean, a deep-sea fish of the Gulf 

 Stream. Family Cera/iidtr. 



greatly diminished or wholly diverted the Gulf Stream, which 

 carries warmth from the tropics to the northern Atlantic and 

 northwestern Europe.' 



Fig. 181.— Excrpes asper Jenkins and Evermann, a fish of the rock-iiools, 

 Guayraas, Mexico. Family Blenniidce. 



"Any very recent means by which the fishes could have 

 passed readily from one side to the other would have resulted in 

 making the fish faunas of the two shores practically identical; 

 but the time that has elapsed since such a waterway could have 



