248 PROCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



The case of Jacosta {Cernuella) virgata (Da Cost.) is an extremely- 

 interesting one. At the present day it is very c.mmon throughout 

 the whole of England, and one would naturally infer that it is a true 

 native, but the geological evidence tells a very different story. 

 Common in the early Holocene beds of Cornwall and Devon, else- 

 where it is practically absent from all Holocene deposits, the 

 exceptions being Cleeve Hill, Gloucestershire, of Late Celtic age, 

 and St. Catherine's Down, Isle of Wight, a deposit that sadly wants 

 re-investigation. The Chalk districts of Kent and Surrey are 

 particularly favourable to this species, yet it is absent from every 

 rain-wash, whether pre-Roman, Roman, or later. It is true that 

 the growth of tilth has been beneficial to the species, but there must 

 have been very large areas of cornland in Roman times, yet this 

 species is always absent from Roman deposits. The only conclusion 

 is that over the greater part of England Jacosta {Cernuella) virgata 

 (Da Cost.) must be considered a very modern immigrant, certainly 

 within the last three or four hundred years. 



Jacosta (Candidula) caperata (Mont.) has an exactly similar 

 geological history, occurring as a fossil only in Cornwall and Devon- 

 shire. Elsewhere it is absent, except a doubtful record from 

 St. Catherine's Down. One can only conclude that the duration 

 of residence of this species also is a very limited one. I am quite 

 at a loss to account for the rapid dissemination of these two species, 

 and we know too little of their life histories to speculate with any 

 degree of certainty. 



Jacosta (Candidula) gigaxii (Pfr.), unlike the preceding forms, 

 is not a western species. It has occurred in several deposits in 

 Kent, Surrey, and Sussex, and one of these, Northfleet, is certainly 

 pre-Roman. It is, however, decidedly rare as a fossil, and it is 

 only since Roman times that it has been able to extend its range 

 to any great degree. It may possibly be an introduction into 

 England by human agency in late Celtic times, for it is quite absent 

 from all early Holocene deposits. 



Theha cantiana (Mont.), though so abundant at the present day, 

 owing to its absence from all pre-Roman and Roman beds, must be 

 considered a modern introduction, and one is tempted to suggest 

 that it arrived here in Norman times. It occurred in the Ightham 

 fissure in close proximity to the bones and bell of a ferret, a good 

 example of the doubtful value of unsupported cavern evidence. 



Helix aspersa, Miill., is extremely common in all Roman deposits, 

 and examples were found in London in the crevices of the Roman 

 Wall. Its size prevents its being overlooked by the archaeologist, and 

 hence its recorded occurrences with Roman objects are numerous, 

 whilst this association has on more than one occasion been the cause 

 of its being labelled " Roman snail ", with the added information 

 for the benefit of the public that the scientific name was " Helix 

 pomatia " ! It occurs in the early Holocene of Cornwall and Devon, 



