“…This suggests that the threshold velocity of Nautilus shells is nearly constant, regardless of bottom type. Table 2 and Figures 3 and 4 show the results of the experimental phase on restraint orientation: (1) most shells Abbreviations (see also Masuda et al, 1999;and Davis, 2002); , mean restraint direction; , mean resultant length; d 0 , confidence interval for R mean direction ( pϽ0.05). (2) the orientations exhibit nearly bilateral symmetry-the orientation range for shells with their left sides upward was 180-190Њ, and for those with their right sides upward was 170-180Њ; (3) larger shells showed a stronger preferred orientation; (4) shells where the body chambers were cut artificially showed a wide array of orientations; (5) the numbers of shells with left or right sides upward were nearly identical; (6) shells with their left side upward tended to settle on the right half of the flume, facing downstream, and vice versa (especially for larger shells; Fig.…”