THE LAND GASTROPODA IN THE NORTH ATLANTIC REGION 169 



distribution; to some extent this conclusion is also based on subfossil records 

 (cf. Pilsbry, 1939, p. 8, and references given by him). Lindroth (1957, p. 234, 

 etc.), however, finds the evidence weak and incomplete and suggests an 

 entirely anthropochorous origin. A supposed Pleistocene fossil thus may 

 equally well be of 19th century origin. 



There is no doubt that part of the population is of a recent anthropochorous 

 nature. On the other hand, radiocarbon dating shows that the species is 

 definitely of pre-Columbian age in Nova Scotia (Clarke and Erskine, 1961 : 

 700 ± 225 years; later dating 600 ± 45 years B. P., according to a personal 

 communication by Clarke). This may be thought to speak in favor of the old 

 idea of dispersal by aid of the Vikings. That idea, however, is nothing more 

 than an entirely unproven hypothesis and, furthermore, there exists no 

 positive evidence that the Vikings ever visited Nova Scotia. The actual 

 shells of C. hortensis were found in the camps of the Micmac Indians. When 

 these matters are considered the statement of their pre-Columbian age 

 evidently is in favor of an old, indigenous occurrence. 



With regard to the possibility of passive dispersal, an indigenous American 

 occurrence is not definitely excluded. It is not difficult to raise various hypo- 

 theses, regarding the recent area as relic, due to dispersal via Greenland- 

 Labrador during a Post-glacial period, or even an Interglacial one. But owing 

 to lack of really conclusive evidence it is very unproductive. The only way to 

 solve the problem of C hortensis — which would be of certain interest owing 

 to its crucial significance — is new, careful field research, by which special 

 regard must be given to the existing rich experience of the ecological occurrence 

 of C. hortensis in Europe. 



For land gastropods a solution of problems of this kind evidently is 

 attainable. Owing to the slow rate of estabhshment, also when highly favored 

 by passive dispersal, introduced gastropods very long maintain an immature 

 pattern of distribution. Practically always, it seems possible to give a definite 

 answer to the question whether or not a species is introduced into an area, if 

 only its distribution on an ecological basis has been accurately clarified. 



A field survey would result in a more correct picture )of several further 

 species ( Vallonia pulchella and costata, Vertigo pygmaea and alpestris, also the 

 above-mentioned Limax marginatus) whose faunistic state in northeastern 

 America is yet obscure. Of course, the distribution and history of the endemic 

 American gastropod fauna would also be elucidated. 



Surprisingly, the interchange of endemic gastropod species in the North 

 Pacific territories seems to be very limited. The American Zonitoides arbor ens 

 and Hawaiia minuscula, according to Licharev and Rammelmeyer (1952), 

 have an inconsiderable spontaneous distribution in the Far East. The prepon- 

 derantly Siberian Succinea strigata reaches Arctic North America.* It is not 



* Pilsbry (1948, p. 811) cites S. strigata from Igaliko Fjord, Greenland. However, the 



actual sample, by revision, has proved to belong to Succinea pfeifferi subsp. groenlamlica. 



