The predatory boring habit common to many recent snails probably arose first in the Polinicinae (Naticacea) during Upper Cretaceous (Cenomanian) times (100 million years B.P.) . In the fossil record the frequency of bored shells increasesgreatly in rocks of latest Cretaceous age and becomes more widespread during early Tertiary times coincident with the major diversification of the primary groups of boring snails. The borings in these Cretaceous and Tertiary shells show the same characteristics of preference of penetration in one pelecypod valve rather than the other or in position of the boring site on the shell that are found in recent shell assemblages. Borings in Paleozoic brachiopod shells (230–550 million years old) that have previously been attributed to gastropod predation are herein attributed to other but unknown boring organisms. In part these borings are not accepted as evidence of Paleozoic gastropod predation because it necessitates: (1) Postulation of the separate development of a boring habit ith its concomitant development of an accessory boring organ in a groupwhose descendants are all herbivores, and (2) The development of such a habit hundreds of millions of years before the appearance of any relatives of present day borers.