Biometrical Observations on Shells ofLimnaeaSpecies

In differentiating between species of snails various ratios of shell dimensions are frequently used as biological constants descriptive of the species. Some of the ratios commonly used are: length to breadth (L/B), length to length of body-whorl (L/W), length to length of shell aperture (L/l), and length of shell aperture to its breadth (1/b). Mean and extreme values of these ratios are given for small samples of five species ofLimnaea. 2. InL. palustristhe least variable of these simple ratios is L/W and the next best is L/l. Statistics are given for the distributions of these two ratios. 3. Data collected by Mozley are used to show that inL. palustristhe ratio L/l (at least) is subject to considerable local variation, a fact which detracts from its value as a species constant.