Page:Popular Science Monthly Volume 68.djvu/527

Rh. If there was a continental mass connecting South America with New Zealand and Australia fit to be inhabited by fishes, there must have been an abundant and diverse fish fauna which has disappeared. If the antarctic continent depended entirely for its existence on the evidence from the distribution of the fresh-water fishes, its existence would be very highly theoretical and precarious.

However, the evidence from other sources of a former land connection has become conclusive, and I am of the opinion that during the submergence of large parts of Patagonia during the late Pliocene the formerly abundant fresh-water fauna became exterminated, with the exception of those that were indifferently fresh-water or marine.

The Petromyzontidre offer still another difficulty. There is no place on the American continents between the Mexican plateau and Central Chile that harbors any species of the family. The northern and southern species belong to distinct genera. At least two of the South American genera are peculiar while two others are found in Australia and New Zealand.

 8. The Similarity of the Tropical American to the Tropical African Fauna and the Necessity of and Evidence for a Former Land Connection between Africa and, South America.

North America has not contributed a single element to the freshwater fish fauna of South America. Two prominent South American families, the Characiniclæ and the Cichlidæ, have representatives as far north as the Rio Grande basin, and one of these has succeeded in crossing over into Cuba, evidently from Yucatan; on the other hand, several members of the North American fauna have representatives as far south as the Isthmus of Tehuantepec. The North American fauna is entirely distinct from the tropical American fauna.

But four genera of fresh-water fishes of South America north of Patagonia are found in any other continent than North America. These are Synbranchus, Agonostomus, Cotylopus and Fundulus. The first found also in brackish water, the second belonging to the marine family, Mugilidæ and the others to the Pœciliidæ. Synbranchus is found in India, Agonostomus in middle America, the West Indies, northern South America and New Zealand, Australia, Celebes, Mauritius and Comoro Islands. There is no reason why Agonostomus may not have been independently evolved in the South Sea and in America from marine Mugilids. Cotylopus is found in Central America and Reunion and Fundulus in America and Europe.

It is possible that Pimelodus is found in Africa and Pseudauchenipterus in Madagascar. Both are found in South America.

Africa and South America have two groups of families in common. The first group comprises the Serranidæ, Sciænidæ, Mugilidæ and Tetraodontidæ.