The science of or paleophycology has been developing at a somewhat slower rate than most of the other branches of paleontology. Identifications of in various states of fossilization, and, especially, their classification with the living algal phyla by paleobotanists were frequently severely criticized by phycologists. While this criticism, was, at times, so severe as to border on discouragement, it served, on the other hand, a useful purpose in making paleontologists conscious of the complexities involved even in the study of the living and their taxonomy, and it cautioned them to a more reserved and discriminate attitude in regard to determination and classification of marine plants. Modern critical analysis of the systematic standing of many fossil algae described in the early papers by Hall, Walcott, and others showed how questionable is their reference to algae, and especially to definite algal phyla, and it is now realized that even some of the finest recent microscopic work on algae, such as that by Reis (1923) and Bradlev (1929), did not solve unequivocally the problem of their relationship with particular living (see the criticism by Fritsch 1935, p. 12). Fritsch demonstrates that some fundamentally similar types of somatic organization developed independently in more than one order of living algae, and therefore, the morphology of simply organized generally cannot be used, without additional evidence, in an attempt to trace their phyletic relationships. One of the additional critical characters would be pigment, so widely used in the principal division of the living algae-but this evidence is lacking in the material. Another would be types of fructification-but these too are absent in the great majority of algae. Of other criteria for precise identification there remain only detailed anatomical structure, which is seldom observable, and a combination of various morphological features in a complex algal soma which may provide reasonable evidence for a natural classification of algae. The fossils which have been classified as with a varying degree of probability may be conveniently grouped, for the sake of the following brief discussion, in four major categories: