. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 486 Bulletin uf Comparative Zoology, Vol. 138, No. 7. Figure 23. Correlation of shell thickness (callus) and climate in western (left) and eastern stocks of P. bermudensis zonafus. SH := Shore Hills; H ^ Harrington; P ^ Pembroke; SG :=z St. George's; S =^ Southampton. b) shell size: i) maximum size: With a range of maximal shell size far smaller than that of P. nehoni or P. cupula, little can be done with this variable in F. bermudensis due to great differences in sample size. I can state with fair certainty
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. 486 Bulletin uf Comparative Zoology, Vol. 138, No. 7. Figure 23. Correlation of shell thickness (callus) and climate in western (left) and eastern stocks of P. bermudensis zonafus. SH := Shore Hills; H ^ Harrington; P ^ Pembroke; SG :=z St. George's; S =^ Southampton. b) shell size: i) maximum size: With a range of maximal shell size far smaller than that of P. nehoni or P. cupula, little can be done with this variable in F. bermudensis due to great differences in sample size. I can state with fair certainty only that the largest Shore Hills snails surpass those of all more recent populations in maximal size. For more recent forms, I compiled means for the five largest specimens in each sample. The only consistent result of this procedure is the artifact that larger samples tend to have larger mean \alues. Grand means for each post-Shore Hills formation are: Harrington, mm; Pembroke, ; St. George's, ; South- ampton, The largest St. George's sample (Spittal Pond, locality 32) has fewer specimens than any of the measured interglacial samples. If the sample-size artifact controls values of the grand means. then an unbiased sampling procedure might predict that St. George's specimens tend to he somewhat larger in maximal size. ii) standardized size-at-fifth-whorl: Par- allel oscillation of size-at-fifth-whorl and lithologv is pronounced and consistent (Table' 12, Fig. 24). Values of this measure are low in red soils, intennediate in unindurated zones (Harrington) and high in eolianites (Pembroke, Southamp- ton). In three localities, Harrington and Pembroke snails were found in continuous sequence, inches apart in direct superposi- tion—a strong indication that genetic conti- nuity was maintained during the lithologic transition. In all cases (P. ]). zonatus from Whalebone Bay, locality 1, and Towai Gut, locality 87, and P. b. sieglindae from Rocky Bay, locality 44)
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