Note 350 — Chapter XI
Reading edition
In equivalve bivalves the animal lives in an upright position. In inequivalves, i.e. one large and one small valve, the animal lies on its side. The situation of bivalve shells, as oysters, should therefore be noticed, for if they lie on their concave shell, with the flat valve uppermost, it is evident they were overwhelmed in their native bed and in a living state; if they lie indiscriminately on either valve, they were probably dead shells and overwhelmed in that state. If the pallial imprint is notched by a sinus, it shows the presence and size of the tubes of the mantle. Whether there be one or two muscular impressions is of far less importance.
[351] For an extended notice of the geographical distribution of testacea, see Prof. Edward Forbes, British Marine Zoology, Part I. p. 141.