REPTILES AND BATRACHIANS The only orders of the great class Reptilia, which are represented by- living species in Great Britain, are the lizards [Lacertilia), and the snakes or serpents [Ophidid). On the mainland of Great Britain we have three species of lizards, and three species of snakes, six species in all of reptiles. In addition to these, two other species occur in the Channel Isles, the green lizard {Lacerta viridis) and the wall lizard [Lacerta muralis), so that if these isles be included in the term Great Britain we possess five lizards. Neither the green lizard nor the wall lizard, however, is indigenous to the mainland, although some escaped specimens are now and then captured, the result of the growing custom of keeping these creatures as pets in captivity. Of the three snakes, the adder (Vipera berus) occurs in every county in England, Scotland, and Wales, but not in Ireland. The grass or ring snake [T'ropidonotus natrix) is common in most English counties, becoming rarer as we go north, and in Scotland occurring only in Roxburghshire and Berwickshire, absent also from Ireland. The rare smooth snake {Coronella austriaca) is restricted to the southern counties of Dorset, Hants, Surrey, and Berks. In Herefordshire the slow-worm or blindworm is by far the most common lizard [Anguis fragilis), the common viviparous lizard being much more local, and in many parts of the county absent [Lacerta vivipara). The sand lizard [Lacerta agilis) does not occur. In this county, therefore, we have four reptiles, two snakes, and two lizards. It so happens that there is probably no county in Great Britain in which so much attention has been paid to the reptile fauna, as the county under notice, for it was within its area that the present writer carried out an extensive series of observations extending over a period of seven years, only the briefest summary of which can here be mentioned.^ The distribution of the adder and the ring-snake within the county seems to be determined by physical conditions. Thus the harmless ring- snake is found fairly commonly in the flat district where the land is well wooded, in company with the adder. Towards the mountainous southern border, especially in the district of the Monnow Valley (which divides the county from Monmouthshire) the ring-snake disappears, and the adder becomes more common. This is obviously a matter of immunity from ' See Brit. Serp. (Blackwood), Brit. Lizards (Upcott Gill), Reptile Studies, The Field 'Naturalist^ Quarterly, and various papers in the Transactions of the Woolhope Club and the Royal Physical Society of Edinburgh, by G, Leighton, M.D. 127
