Land snails - Stephen Carter.

Introduction.

Land snails were recovered both by hand collection on site and by flotation and wet sieving of soil samples. Hand collections were only made in the 1990 excavation season and therefore there are none from contexts 1157. As with all hand collection of land snails, only the larger species are recovered and in this case there is only one. Shells from soil samples were collected in either a 300 m mesh if they floated or a 1 mm mesh if they were wet sieved. It is usual practice to collect land snails with a 500 m mesh sieve so in this case the 500 m to 1 mm nonfloating fraction is missing. The shells were identified using the author's own reference collection; nomenclature follows Kerney and Cameron (1979).

Results.

The assemblages from soil samples are listed in table 1. Only 22 samples contained land snails (a small proportion of the total) and the numbers of shells in each assemblage was also very small. Five species were identified but only two, Vitrea contracta and Oxychilus cellarius occurred in the majority of samples. All shells were in a subfossil condition except for the two shells of O. cellarius from context 652 and one shell of V. contracta from context 28.

Hand collections of land snails consisted of up to 8 shells of Arianta arbustorum from each of the following contexts: 201, 5.1; 235, 5.2; 237, 5.2; 263, 7.1; 268, 7.1; 507, 7.1; 510, 7.1; 539, 7.4; 540, 7.4;; 543, 7.1; 570, 5.2

Discussion.

The small number of assemblages, despite an extensive sampling programme, shows that land snails have not been preserved in the majority of contexts. Those contexts with land snails are part of blocks 2, 5, 6 and 7 in Area 5 with 17 out of a total of 29 from block 7.

Calcium carbonate content results show that these contexts are no more calcareous as a group than the site as a whole, therefore conditions for preservation are apparently no better. This suggests that land snails are not preserved in any context for long periods and those with shells were accessible in recent times to snails at the surface. The presence of modern shells of the two commoner species supports this interpretation as does the fact that all the species except Cochlicopa lubrica are known to penetrate loose rubble (Evans and Jones, 1973). The higher proportion of block 7 contexts with land snails reflects the loose stony nature of these deposits. The only example of C. lubrica comes from a modern (block 1) context.

The presence of Discus rotundatus is interesting as there are no records for this species in Shetland in the Atlas of Non-Marine Mollusca (Kerney, 1976). The species list given in Berry and Johnston (1980, 313) does include D. rotundatus but fails to quote any sources so its current status is unclear.

Conclusion.

The few small assemblages of land snails from Iron Age deposits at Scalloway are the result of recent penetration by four species from the modern surface. They do not provide any information about the Iron Age environment or even a species list for that period.

Table 1 Land snail assemblages recovered from samples by flotation and wet sieving
Context   Block     Sample     Discus     Vitrea     Oxychius     Cepea/    
                     Vol     rotundatus  contracta   cellarius    Arianta   
                    (ltrs)                                                  

   8        1         14                     3                              

   9       7.4        12                     4           1                  

   14      6.2        14                                 1                  

   17      7.7        72                     2                              

   28      7.4        5                      4           4                  

   29      7.4        14                                14                  

  152       1         10                     2           1                  

  237      2.1        14         28         12           3           4      

  260      6.1        13                     1           1                  

  266      2.1        12                                             1      

  274      7.1        14                                 1                  

  283      7.1        13                     3                              

  507      7.1        13                                             1      

  531      2.1        13         1                                          

  570      2.1        13                     1                       1      

  635      7.4        14                    17           3                  

  652      6.2        12                                 2                  

  654      7.4        12                    45           3           1      

  680      7.5       209                     1                              

  686      7.2        12                     1           2