MOLLUSCS NON-MARINE The non-marine mollusca are plentifully represented in Kent, the physical features of the county being eminently favourable to their development. The terrestrial forms are more abundant throughout the northern portion, or chalk district, than in the sandy and clayey areas verging on the Weald, and find those varied conditions of bare dow^n, or wooded dell and hedgerow, that suit the different requirements of the several species. One of these, Helicella cantiana, takes its name from the county, though this ' Kentish snail ' is by no means confined to this area : it was apparently a late introduction into these islands, for it has not yet been found in any but the most recent post-tertiary deposits. The aquatic forms are nearly all present and abound in the numerous ponds and streams as well as in the rivers ; while the salt-marshes and estuaries of the coast provide suitable habitat for the brackish-water forms. The literature on the subject is very scattered, and consists mainly of lists relating to isolated localities or notes concerning isolated occur- rences. The most comprehensive paper is that on the ' Land Mollusca of Kent,' by A, Santer Kennard {Kent. Mag. 1896, i. 418). From these sources and the Records of the Conchological Society the sub- joined list has been compiled. Of the 139 species occurring in the whole of the British Islands, no less than 1 1 1 may be met with in Kent. Among this number no account is taken of such records as Helix pisana, alleged to have been found near Folkestone, that was most probably only one of the endless varieties of the somewhat similar Helicella virgata. Nor is Clausilia biplicata counted, two examples of which were found in rejectamenta on the shore of Dartford Creek, whither they had probably been wafted by the Thames from some locality much higher up on its course. Still less is any notice taken of the Helix cantianiformis, a name bestowed by a French con- chologist on some unimportant variety of the ' Kentish snail.' Nor has Vivipara contecta been included, though it once swarmed in a pond at Beckenham, since filled in, where it was apparently introduced. Three other species occur in post-tertiary deposits of the county that have not yet been met with living in the district, viz. : Vertigo antivertigo, V. pusilla and Succinea oblonga. The first two may have been drifted down to their present place of sepulture, but the last-named was certainly at one time a snail of Kent. 99
