13. Vipera berus (as far north as 64°).
14. Ancistrodon halys (south, between Volga and Ural).
Without attempting anything like a complete bibliography, we have compiled a list of faunistic works and papers dealing with the snakes of Europe:
Europe in General
Schreiber, E.: Herpetologia Europæa. Zweite Auflage, Jena, 1912, 8vo.
Steinheil, F.: Die Europaeischen Schlangen. Kupferdrucktafeln nach Photographien der lebenden Tiere. Jena, 1913, 4to. (in progress).
Great Britain
Bell, T.: A History of British Reptiles. 2nd edit., London, 1849, 8vo.
Cook, M. C.: Our Reptiles. London, 1865, 8vo.
Leighton, G.: The Life-History of British Serpents. Edinburgh and London, 1901, 8vo.