BEESTON : NON-MARINE MOLLUSCA OF LLANDUDNO. I39 



torion { = ifa/a)." Two years later, 1886 {/oierji. of Conch., vol. v, 

 p. 28) Mr. Tomlin, in recording H. ttaia, says : — " Plentiful, but 

 local, in various parts of the Morfa with var. alba. I am rather sur- 

 prised that Mr. Roebuck missed H. ericetoruni, as it seemed well 

 disseminated, though not ubiquitous, on the Morfa." It is rather 

 strange that my experience should coincide with that of Mr. Roe- 

 buck. I spent three weeks in 1901, and the same in 1915, at 

 Llandudno, but failed to discover a single shell with the exception 

 of one dead specimen, which I picked from the side of a section of 

 sand-hill, quite a foot from the surface. My conclusion is that, for 

 some inexplicable reason, the species is very erratic in appearance, 

 and Mr. Tomlin was fortunate enough to find it when the animals 

 were plentiful and on the crawl. There are evidently climatic or 

 other causes, which, if we only knew, will account for the phenomena. 

 In any case, the animals are almost (in some cases quite) extermin- 

 ated for a considerable time. If such untoward accidents (parasites, 

 severe frosts, increase of birds, rodents, etc.), occur, it would take 

 several years for a once-thriving colony to recover itself. An instance 

 of this kind occurred in my experience a few years ago. On the side 

 of a somewhat bare down, I found dead shells of H. itala for several 

 seasons in succession, but no live ones, although I searched under 

 all kinds of climatic conditions. For two or three years I did not 

 visit the place, but one -muggy, damp day I found a large number 

 crawling about, most of them in one small area. The following 

 season the animals had greatly increased and spread, and continued 

 thus for two or three years afterwards. Then they again apparently 

 disappeared, and only dead shells were to be found for several 

 seasons. Again followed a resurrection, beginning with a few indi- 

 viduals, which have since increased to a fair-sized colony. In this 

 instance probably two or three nights' continuous frost nearly anni- 

 hilated the snails which were most exposed, only those escaping 

 which were hibernating or in some degree protected. Late autumn 

 seems to be the season when this snail exposes itself most, and is 

 thus affected most severely by sudden changes of temperature. May 

 not something of this kind happen to H. itala at Llandudno ? 



var. alba Charpentier. — Found with type (Tomlin). 



Heiicella caperata (Montagu). — Common. Sand-hills and golf- 

 links. Great Orme, Conway Road, Nant-y-Gamar Road, 

 Llandrillo, Rhos Fynach, Llangwystenin, Llanrwst. 



var. ornata Picard. — Great Orme. 



var. alba Picard. — Morfa (one specimen). 



Heiicella heripensis Mabille. — Conway Road (one specimen). 



