714 Hans GaDow, Mexican Amphibians and Reptiles. 
oceur in the hot zone cannot of course be considered as Arctic 
„derelicts“. Lastly let us enquire into the affinities of the species. 
Sceloporus scalaris with aeneus, and S. microlepidotus each stand 
rather by themselves in this genus and are moreover typically and 
exclusively Mexican. 
Gerrhonotus imbricatus, and its nearest relations, are confined to 
Mexico, whilst the widely distributed @. coeruleus, Vancouver to Cen- 
tral America does not seem to ascend very high. 
Orotalus triseriatus is the high-mountain species of Mexico, whilst 
on the plateau it is represented by the closely allied ©. polystictus 
out of which it seemes to have been developed. 
Tropidonotus scalaris is entirely Mexican and the same applies 
to its closely allied ©. scaliger. 
Spelerpes leprosus, with its ally S. belli, and S. orizabensis are 
Mexican only; and so is S. chiropterus, but this has its nearest allies 
in the Eastern and South Eastern parts of the United States. 
Thorius, a monotype, is the sole representative in Mexico of the 
Desmognathinae, the original home of which group seems to be the Eastern 
half of North America. The same seems to apply to Spelerpes, but 
our general conclusion is that whatever has been received by Mexican 
mountains from the States, be it genus or species, has there been 
modified into a Mexican species, distinet enough not to be mistaken 
for a derelict. 
In short the inhabitants of the alpine zone of Mexico have been 
developed there out of other species established at a lower base, 
unless they have, like Tropidonotus simply ascended without under- 
going any specific changes. 
Nor can it be said that the strietly alpine species of Mexico 
have developed an arctic or boreal facies, an idea which is scarcely, 
if at all, applicable to Reptiles and Amphibia, but they have acquired 
boreal habits, if as such be considered hibernation, endurance of 
cold and moist ground, and in connexion therewith viviparous habits. 
It is at least significant that out of the 12 species found at or above 
the 10000 ft. level all except Thorius and Troptdonotus, happen to 
belong to viviparous genera, and that of the genus Sceloporus which 
varies in this respect, S. scalaris, S. aeneus and 5. microlepidotus are 
viviparous. 
Cambridge, June 1910. 
Lippert & Co. (G. Pätz’sche Buchdr.), Naumburg a.S. 
