parallel to the North Cliff SN 132 010) to beyond the boundary of Tenby (SN 128 025). Old empty shells were found in the earth of the roadside bank as far inland as the point where this road joins the main road out of Tenby (about 1 km inland). Living specimens were only found on a 20 m length of the northern (i.e. south-facing) bank of the road, opposite The Glebe. No more than seven were seen at any one time. A further, rather sparse colony was found alongside the south side of Marsh Road, for a distance of about 500 m opposite the County Secondary School. Snails were found in the low vegetation (up to about 50 cm) which extends beyond a low Fig. 4 Theba pisana resting on alexanders. wooden railing set back about 2 m from the road, the area between the road and this fence being short grass. Discussion and conclusions The most striking change to have taken place in the distribution of T. pisana in mainland Britain since previous accounts is the reduction in abundance on the Tenby Burrows, and the apparent absence of the species from Manorbier (last recorded by Deblock, 1962) and the cliff-tops from Giltar to Lydstep (cf. Stubbs (1900) and Wintle (1925) who both indicated the species in profusion on the Burrows, although whether it was particularly abundant on the cliff- tops was not said). Its complete absence from the half of the Burrows nearer to Tenby itself is certainly the result of the planting of sea buckthorn in about 1940 (Stratton 1970). Little other vegetation is present and it therefore no longer provides a suitable habitat for T. pisana. The development and increased use of the golf links has undoubtedly also contributed to its demise in this area. Barrett (1972) indicated how trampling of areas of marram and cutting of the vegetation excluded T. pisana from otherwise apparently suitable areas in Guernsey. Manorbier Bay is a popular beach during summer; a large area behind the beach itself is used as a car park, and the dunes around the Bay are heavily used by people. This may well be significant in the apparent extinction of T. pisana here. There is little suitable habitat on the cliff-tops from Giltar to Lydstep. These cliff-tops are trampled by people, and both sheep and cattle graze right to the edges along parts of this section of coast. Chappell et al. (1971) showed how trampling can change the habitat and hence the associated snail fauna; Morris (1968) indicated similar changes due to grazing. The short turf which results is unsuitable for T. pisana (see Barrett 1972). Humphreys (1976) did say that the area inhabited by T. pisana at St. Ives in Cornwall had the appearance of a 'short, dense grass sward', but the same area, observed in 1979 was covered with mixed vegetation up to 50 cm high, a relatively normal habitat for T. pisana, if not as high as the alexanders and sea radish it is often associated with at Tenby. It is probable, then, that increased trampling and grazing partially account for the extinction of T. pisana along these cliffs. The colonies on Caldey Island are subject to considerable human interference during the summer
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