A remarkable fact in the distribution of European Snakes is the altitudinal range of _Vipera berus_, _V. aspis_, and _V. ursinii_. The first being the northernmost snake, generally distributed in Northern Europe and more locally in the south, should, one would expect, be a mountain form in the south. This is so in Switzerland, where it occurs chiefly between 2,500 and 9,000 feet, on the northern aspect of the Alps, whilst _V. aspis_ lives at altitudes below 5,000 feet; but on the southern aspect of the same chain things are reversed, and _V. berus_ is replaced by _V. aspis_, which reaches an altitude of 9,700 feet, whilst the former shows a tendency to abandon the mountains, and has established itself in a few localities in the plain of North Italy. Again, in France _V. berus_ is the northern and _V. aspis_ the southern species, yet the latter is the only one found on the French side of the Pyrenees (up to 7,250 feet), whilst the former reappears in North-Western Spain and Portugal at very low altitudes, even at sea-level. _V. ursinii_ is a mountain form in Italy (Abruzzi), in France (Basses-Alpes), and in the Balkan Peninsula (up to 6,800 feet); but it is restricted to the plain in Lower Austria and Hungary, where _V. berus_ occurs only in the mountains. Only three species are entirely confined to Europe: _Coluber scalaris_, _Vipera ursinii_, and _V. aspis_. Of the species which range outside Europe, the following occur both in Western Asia and in North Africa: _Eryx jaculus_, _Tropidonotus natrix_, _Coelopeltis monspessulana_, _Vipera lebetina_. In Western Asia and the North-East of Egypt: _Tropidonotus tessellatus_, _Zamenis dahlii_. In Western Asia: _Typhlops vermicularis_, _Zamenis gemonensis_, _Coluber quatuorlineatus_, _C. dione_, _C. longissimus_, _C. leopardinus_, _Coronella austriaca_, _Contia modesta_, _Tarbophis fallax_, _T. iberus_, _Vipera renardi_, _V. berus_, _V. ammodytes_, _Ancistrodon halys_. In North Africa: _Macroprotodon cucullatus._ In North-West Africa: _Tropidonotus viperinus_, _Zamenis hippocrepis_, _Coronella girondica_, _Vipera latastii_. The following lists will help to elucidate the distribution of the snakes in the different parts of Europe: I. SCANDINAVIA 1. _Tropidonotus natrix_ (as far north as 65°). 2. _Coronella austriaca_ (as far north as 63°). 3. _Vipera berus_ (as far north as 67°). II. GREAT BRITAIN 1. _Tropidonotus natrix_ (England and Wales, extreme south-east of Scotland). 2. _Coronella austriaca_ (Surrey, Berkshire, Hampshire, and Dorsetshire). 3. _Vipera berus._ III. BELGIUM AND HOLLAND 1. _Tropidonotus natrix._ 2. _Coronella austriaca._ 3. _Vipera berus._ IV. GERMANY AND DENMARK 1. _Tropidonotus natrix._ 2. _Tropidonotus tessellatus_ (Middle Rhine and Moselle, Saxony). 3. _Coluber longissimus_ (Denmark, Schlangenbad, Treves). 4. _Coronella austriaca._