Molluscan Assemblages from the Marine Middle Miocene of South Jutland and their Environments. Vol. II.

Abstract

Although the number of species in which variation of shape has been investigated is relatively small, due to the broken state of the material, it is possible to outline some new fundamental features of shell morphology.

The investigations of Yoldia glaberrima, Leda Westendorpii, Leda pygmaea, and Spisula subtruncata indicate that the length/height ratio of pelecypod valves is very seldom constant throughout the life of the animal. This is important, but some workers are apparently not aware of this principle, to judge by the significance which is often attached to the calculation of means of length/height ratios, or other quantitative expressions of shape. Mean values of this sort have no taxonomic significance unless they are accompanied by information on the size groups of the shells measured.