Researches on the foraminifera. Supplemental memoir. On an abyssal type of the genus orbitolites ; a study in the theory of descent

This paper is supplemental to the series of Memoirs formerly presented by the author on the structure of certain of the higher forms of the group of Foraminifera; in which he laid down the new principles of classification afterwards worked out by him, in conjunction with Messrs. W. K. Parker and T. Rupert Jones, in his “ Introduction to the Study of the Foraminifera;” and especially to the first of those memoirs (“ Phil. Trans.,” 1856), which consisted of a Monograph of the genusOrbitolite s, and of some general doctrines deduced from the study of it as to the Range of Variation in Species, a question which was much occupying the attention of philosophical naturalists. The subsequent publication of Mr. Darwin’s “ Origin of Species ” having led him unhesitatingly to adopt the principle of “Descent with Modification ” or “ Genetic Continuity,” he had applied it to the construction of a pedigree of theOrbitoline type ; between the smallest and simplest, and the largest and most complex of which, he had shown in his first memoir that such “ continuity ” could be clearly traced out.