250 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



abundantly in tlie neighbourliood. Ena ohscura, Miill., too, is another 

 form far more abundant than formerly. 



Lauria cylindracea (Da Cost.) has a marked partiality for old 

 stone walls covered with ivy, and I have never yet seen an old 

 churchyard wall of this description that did not yield this species. 

 The fragility of the shell of Balea 'perversa (Linn.) may account 

 in some degree for its rarity as a fossil, and the lack of suitable 

 habitats may be the cause of the former scarcity of Sphcerium 

 lacustre (Drap.). Though known from the Pleistocene, this last 

 species is absent in the Holocene from all pre-Eoman beds. 



Dreissensia polymorpha (Pall.) has been claimed as an introduction 

 during the early part of last century, but its occurrence as a fossil 

 in a Eoman deposit at Whitefriars, London {Proc. Geol. Assoc, 

 vol. xi, 1890, p. 342), as well as at Clifton Hampden, Oxfordshire, 

 completely negatives this view, and it must be considered a true 

 native, a view which was always advocated by Gwyn Jefireys. To 

 nearly all these species human agencies have been beneficial by 

 increasing their suitable habitats. 



Those species whose area of distribution has apparently diminished 

 are : — 



Theba cartusiana (Miill.). 

 Ena montana (Drap.). 

 Acanthinula lamellata (Jeff.). 

 Lauria anglica (Fer.). 

 Vertigo suhstriata (Jeff.). 

 „ moulinsiana (Dup.). 

 „ alpestris, Aid. 

 „ pusilla, Miill. 

 5, angustior, Jeff. 

 " Truncatellina minutissima (Hart)." 

 Planorhis stroemii, Westld. 

 Acicula lineata (Drap.). 

 Theba cartusiana (Miill.) in Kent is unknown living west of 

 Canterbury, yet it occurs in all the pre-E,oman and Roman rain- 

 washes at the foot of the chalk hills from Otford to Snodland, as 

 well as at Northfleet and Greenhithe, clearly proving that this species 

 was formerly a widely spread and common form in West Kent, 

 whilst linking up this area with its present distribution, it has been 

 found fossil at Hollingbourne. Though unknown living in Essex, 

 it occurs fossil at Harwich and Felstead, whilst it has also occurred 

 in a deposit at Butley, Suffolk, thus proving that the isolated colonies 

 in Norfolk and Suffolk are not accidental introductions, but are the 

 last survivors of a formerly common species. 



Acanthinula lamellata, Jeff., is quite a common form in some of 

 the Essex deposits as well as at Wheatley, Nottinghamshire, and 

 from neither of these counties is it known living. 



Similarly Ena montana (Drap.), known fossil from Reigate, Surrey, 



