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Larger context for LACK in Corpus USbrown_UKbncw/UK_bncw.txt

  Moore (1936) thought that diet influenced shell shape as well as shell colour regarding the development of the wide-mouthedopen- shore form a consequence of a mussel-rich diet.   Nobody has been able to substantiate that idea and Kitching (1977) cites instances in Spain and Scotland of enclaves with elongated shells feeding on mussels.   Crothers (1973) related the resulting gradation in N. lapillus shell shape to exposure on Pembrokeshire (Fig. 24) shores by the expression y= 1.214+0.036 X Where Y is a Shell-shape ratio and X the Ballantine (1961) Exposure Grade. r = 0.878 (Crothers, 1983b).   L Ap &mdash shell length divided by aperture length (Fig. 22) is the simplest, most convenient and most objective measure of shell shape in dog- whelks.   lack >   Although lack ing the intrinsic relevance of " mouth area" ( used by Smith, 1981, for winkles) or of " apical angle" and " whorl ratio" (employed by Kitching, 1976 1977 Cambridge and Kitching, 1982) this ratio is less affected by the absolute size, thickness, age or condition of the shell and it is undeniably easier to record in the field.