DR. H. G. SCHENCK has published an exhaustive monograph of “Nuculid Bivalves of the genus Acila” (Geological Society of America, Special Papers No. 4; 1936). A critical descriptive catalogue of the twenty -five known species and varieties is arranged in the order of their age, from Cretaceous to Recent, and is illustrated by eighteen admirable plates which give a complete iconography of the genus. The systematic part of the work is preceded by the morphology of the shell and by an account of the anatomy, habits and habitats of the living animal. The terms ‘paleo-biology’ and ‘biostratigraphy’ are used hopefully, but no radically new methods are apparent to correspond with them. Ever since palaeontology has been rationally studied, its best workers have used the anatomy, the habits and habitats of living creatures to explain the debris of their precursors. The method requires caution, for some animal genera have changed their mode of life. The marine mollusc Pholadomya, for example, is now abyssal; in Jurassic times it lived in shallow water and, so late as the Eocene, it is found in sediments which give no indication of very deep seas. Dr. Schenck was led to this study by the problems of the Oligocene in the United States Pacific coastal areas. His results help to solve these problems, not by any a priori palseo-biology, but by the accurate delimitation of fossil species and by showing that they are associated with distinct faunas in a sequence of strata. This is not a new method, but it is the only sound one, for all our knowledge of the succession of forms of life is from stratigraphy, which, somewhere or other, must be based upon visible superposition. Terms like ‘zone’, ‘age’, ‘epoch’ are discussed. Palaeontologists did not invent these words, which are still current in ordinary speech, so that we can doubt the wisdom of restricting their meaning, for their common, vague sense is sure to lodge in runaway minds and cause confusion.