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Show 2 0 2 DR. II. GADOW ON MEXICAN [June 6, these have become, or are becoming, too attractive for them, with the result that A. tigrinvm has sunk, or is sinking, into a more or less perennibranchiate state, the Axolotl. Typical Axolotl are those of Lake Xochimilco, the condition of which I have described in ‘ Nature,' Feb. 5, 1903, and Lake Patzcuaro, which, with its rushes, weeds, and other abundance of vegetation, is very similar to the Mexican lake. Sexually ripe Axolotl are also known from Jalisco mountain tarns or lakes, and lastly from St. Mary's Lake, Estes Park, Colorado. It is therefore the combination of certain favourable circumstances (permanence of water, abundance of food, shelter, equable temperature) which produces the " Axolotl." Whoever has seen the very different conditions prevailing in Lake Zumpango, to the north of Mexico City, will easily credit Velasco's statement that A. tigrinvm metamorphoses into the normal gill-less Newt, as it does in the United States, and probably in various other parts of Mexico. All the more interesting is the fact that the other species, A . altcimirani, the only one which lives in the streams of recent volcanic mountains, has been modified into a gill-less but permanently aquatic form. D e sm o g n a t h in ^e .- The three species of Desmognathus inhabit the Eastern United States. Typhlotriton spelceus is restricted to subterranean caves in Missouri. Thorites pennatulus, the only remaining member of this small group, and its sole representative in Mexico, points therefore unmistakably to the Eastern half of North America as the original home of the group, not of Thorius itself. This tiny Newt, less than two inches in length and thinner than a match, with weak limbs and reduced digits, shows a peculiar dimorphism of the size of the nostrils. They are very large and open in the males, much smaller in the females. The lungs are quite aborted as in Desmognathus and Spelerpes. Thorius has a very limited distribution. It was discovered on the south-western slope of the Pic of Orizaba. I found Thorius in abundance on the south slope, 9000-10,000 feet, in high, mixed forest, either on the ground beneath flat pieces of fallen bark, or on decaying logs of pine between the bark and the wood amongst the " worm-meal" of boring beetles and maggots. Again I met them under exactly the same conditions on the Cerro de San Felipe, 8250 feet, near Oaxaca. These are the only two localities so far as we know at present. It is doubtful whether their distribution is now continuous; the watershed between the Atlantic and Pacific, to the west of a line drawn from Orizaba to Oaxaca, averages about 8000 feet in height, and it iswell- Avooded, but there are several deep transverse depressions in it. P l e th o d o n t in ^e.-This group, consisting of 5 genera with about 40 species, is entirely American, with the sole exception of Spelerpes fuse us in Europe. |