BULLEN : MOLLtrSCA OP PEEEANZABUIOE. 249 



(ii) From the small piece of lacustrine deposit remaining in the 

 * sand crater ' west of above deposit 1 obtained — 

 Limncea tnmcatiila (smaller dwarf form). 

 L. sp. {d) ; this may be truncatula, but has no umbilicus and 

 no reflexion of the columella as is usual in that species. 



(iii) From the perpendicular section of stratified sand, and below 

 the level of the small remnant of lacustrine deposit here 

 at about 10 feet away to the eastward, I obtained at 

 a depth of 4 to 7 feet — 



Helicella harhara. 



Vallonia pulcheUa. 



V. excentrica. 



Helix nemoralis (young). 



H. aspersa (young). 



Cochlicopa lubrica. 



Jaminia musconon. 



J. cylind/racea. 



Limncea pereger (young and very small). 



C. — Recent shells or live specimens found in various parts were — 

 Vitrea radiatula. At foot of marram grass in ' crater.' 

 V. alii aria. Ditto. 

 Arion ater. Cliffs at Perranporth. 

 Helix aspersa. Passim. 



H nemoralis. In one spot only, 250 feet o.d, 

 Vallonia pulcheUa. Same habitat as V. radiatula. 

 V. excentrica. Ditto. 

 Helicella eaperata. Passim. 

 H. virgata. Passim. '" 



H. itala. Passion. 



Jaminia cylindracea. At foot of marram grass in ' crater.' 

 J. muscormn. Ditto. 

 Cochlicopa lubrica. Not abundant. 

 Vertigo pygmma. 

 Succinea elegans. 

 S. sp. (may be S. ohlongd). 



Limncea (probably truncatula., dwarf form). Abundant 

 among marram grass in ' crater.' 



From the condition of some of these shells and the probable mixing 

 up of Holocene and recent specimens by the action of the wind, it may 

 be found that some of the shells in this list are not recent, though 

 provisionally put therein. The fragment of lacustrine deposit at the 

 base of the ' crater ' is undoubtedly being destroyed by the wind, which 

 cuts away the softer underlying sand and so causes the projecting 

 shelf of lacustrine deposit to break off, very much as the recession of 

 Niagara Falls is brought about by water action. The shells get 

 detached from their matrix, and are then whirled up the sand-slope 

 until stopped by the line of marram grass. Here the shells can be 

 scooped up in thousands and examined afterwards at leisure. 



