Page:Popular Science Monthly Volume 59.djvu/298

288 The Helices of the West Indies lend no aid to those who advocate the hypothesis of an 'Atlantis' bridging or partially bridging the Atlantic, for they are not allied to species of Madeira, the Azores, Cape Verde or Canary Islands. Their anatomy is vastly nearer Mexican, Californian and East Asiatic groups.

No generalization based upon the distribution of snails, or of any one group of animals, can be satisfactory unless it is supported by the evidence of animals of other groups, and by that of plants. In extending the data relative to the zoogeography of America and Asia, it may be said that the evidence of the naked snails or slugs fully supports that of the Helices. The West American slugs have their cousins in China and the Himalayas, not in eastern North America. The freshwater crayfish of our Pacific slope belong to the Old World genus Astacus, not to the East American genus Cambarus. The evidence of fishes seems to strongly favor a former connection of Asia and America. Thus. Gunther deduces a Central Asian origin for the

Cyprinoids, or Carp family, which is also very numerously represented in America. Moreover, he regards the Chinese species of Catostomus, or 'sucker,' as a return emigrant from America to Asia. The North American catfishes belong to an East Asian group of the family; and our garpike has a representative in Chinese waters.

Such evidence as the higher vertebrates afford do not strengthen the case stated for the snails, because their evolution has been vastly more recent and rapid, and their means of distribution are far less restricted. Thus the horses have attained their present distribution since the Pliocene, but they are capable of spreading rapidly wherever