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Show 204 DR. H. GADOW ON MEXICAN [June 6, for Newts during most of the Tertiary period : on the west the plateau suffering from the volcanic revolutions; on the east the sea still covering the present Atlantic Tierra Caliente. The Cretaceous parts formed so many oases where alone Newts could exist or survive. Later, when the volcanic ranges, even the volcanoes themselves, became covered with forests, the Newts spread onto them, just as they have spread into the moist hot-lands of the State of Vera Cruz. It may appear strange that the limestone should have been the means of their preservation, considering that lime-water is, as a rule, not favourable to their development; but here comes in the significant fact that most, if not all, the Mexican Spelerpes are viviparous, unless they deposit their eggs, like Batrachoseps, in hollow trees. Some of them, for instance S. orizabensis, lead a partially arboreal life. We found many on the pine-trees of Citlaltepetl, favourite hunting and hiding places being the epiphytic plants, especially the large Tillandsias, Orchids, and Philodendron in the hot country forests. The humus and moisture collecting in these growths, often many feet above the ground, swarm with insect life and with little Scolopendras, which seem to be the staple food of these Spelerpes. The apparent absence of Newts on the Northern plateau is most likely due to the dearth of permanent moisture, long-continued periods of drought, and dust. A more difficult question is the apparent absence of Newts on the terrain of gneiss and granite which covers so large a portion of Southern Guerrero and Oaxaca, and on the well-wooded mountains of the Sierra Madre. For months have we searched Guerrero during the rainy season (there are thousands of places which, if they were on the Eastern slope, would yield an abundance of Newts), but it was in vain. A few specimens of S. belli, from the mountain forest of Omilteme, are the only exception. Batrachoseps.-B. scutatus ranges from Illinois to Rhode Island and to the Gulf of Mexico ; the other species live in the Pacific States, from California to Oregon. Quite unexpected was therefore the occurrence of the Californian B. attenuatus on the Nevado de Colima. I found a single, young specimen on the northern slope, at about 7000 feet elevation, in the stump of a decayed pine-tree. There are some patches of granite and of limestone in that district, but then comes an unbroken stretch of originally volcanic formation, for about 200 miles, until the gneiss is reached to the north-east of Mazatlan. We cannot well imagine that this species is an ancient survival; it must be a comparatively recent immigrant from the north-west, from California. Probably it occurs all through the slopes of the western Sierra Madre, which is mostly clad with pine-forests. Resume of the Distribution of Mexican Urodela. All the American Urodela are of Nearctic origin, with their earliest centre in Old Sonoraland. At least the Amblysto- |