Although general percentages for Recent species of bryozoans in Cenozoic faunas have been published by several authors and were reviewed by Stanley (1979), we present percentages calculated from a number of post-1950 faunal studies of Cenozoic bryozoans. Variability among faunas of the same age is not great and the increase through the Cenozoic in the percentage of bryozoan species currently in the modern fauna is monotonic when calculated per million years of each Cenozoic epoch. The 12.5 % of the Recent bryozoan fauna with a fossil record is the same as recorded by Jelly (1889) over a century ago. This contrasts greatly with Valentine's (1989) data (77%) for the fossil record of recent molluscs from the Californian biogeographic province. The average duration of Recent species having a fossil record is 12.2 MY calculated from the midpoint of the earliest Cenozoic epoch in which each species occurs. INTRODUCTION
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Horowitz et al. (1994) studied this question.