During at least a portion of the Permian the Bering portal was open, the Central American closed, the Iberian, Asia Minor, and Bokharan portals open, and the Malaysian portal closed, for the characteristic cephalopod fauna, with Medlicottia and its associates, occurs in Texas, Sicily, the Ural Mountains, Nova Zembla, the Himalayas, and Timor in the Indian Archipelago. The Pacific, or Guadalupian type, on the other hand, is distributed from Japan around the old Pacific shore line to California, and in another gulf across the more southerly part of the American continent to western Texas.
At the end of the Paleozoic era there was much mountain-making, and readjustment of physiography. These disturbances separated some regions that had been united, and joined others that had been divided. In the earliest epoch of the Lower Triassic, the zone of the Meekoceras fauna, the Asia Minor portal, through which the Artinsk fauna had migrated between the western Mediterranean and the Oriental Tethys, was closed, while the Malaysian portal into the Pacific was open. The barrier between the Atlantic and the Pacific still existed in Central America. The Meekoceras fauna is distributed from Spitzbergen, down to India, eastward to Timor in the Indian Archipelago, with a southward arm of the sea extending down to Madagascar, connecting with the Pacific, stretching along the Siberian coast at Wladiwostok, and then across to Idaho and California in the Great Basin Sea.
The next fauna in the Lower Triassic, that of the Tirolites zone, is known only in the Mediterranean Region and in Idaho, the connection being from the Mediterranean-Poseidon Ocean to the Pacific, through the Central America portal, which was temporarily opened by subsidence in that region. All the other portals were closed, so far as we have any information concerning them, this conclusion being based on the provincial character of the faunas of the seas.
In the epoch immediately following, the Columbites zone, is seen the same provincial, or restricted distribution of inhabitants of the seas. The Columbites fauna is found in Idaho, in northern Siberia, and in Albania, but not in India, nor the Oriental Tethys. At this time the Arctic Sea was the center of dispersion, and immigrants went southwestward to Albania, and southeastward to Idaho, but did not reach the Indian waters, in which a different group of inhabitants lived.
In the Middle Triassic the Asia Minor portal and that of Central America were reopened, and the Ceratites trinodosus fauna, with the Mediterranean as its center of dispersion, was distributed westward through the Poseidon-Atlantic to Idaho, and eastward to India. There was also some connection northward to Spitzbergen, and southward to New Zealand, for the binular genus, Daonella, is represented by nearly identical species in all these regions.
In the Karnic horizon zone of Tropites subbullatus, in the Upper Triassic, the same connections still existed, with even closer relation-