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Rh ciples on which its various forms should be classified into Orders and Families; so that among the writings of recent systematists there is a complete disaccordance as to the relative places assigned to them. Having been recently led to inquire into this subject with some care, for the purpose of determining the relations of the Foraminifera to the other members of the class, and having been encouraged to believe that my results may be deemed worthy of acceptance by other Naturalists, I avail myself of the pages of the "Natural History Review" to bring them in a concise form under their consideration; referring to my forthcoming "Introduction to the Study of the Foraminifera;" shortly to be published by the Ray Society, for a fuller exposition of them.

It is not a little singular that Dujardin, who first discovered the true "idea" of the Rhizopodous type, and to whose original account little of importance has subsequently been added, should have so limited his definition of it as actually to exclude some of what we now regard as its most characteristic examples. In his "Histoire Naturelle des Zoophytes Infusoires" (Paris, 1841), he ranks the Amibiens as the second family of his, the Rhizopodes as the third, and the Actinophryens as the fourth; but he distinctly states that the structure of the animal is essentially the same in the first two cases, and that the Rhizopodes are differentiated from the Amibiens solely by the enclosure of their bodies in a testaceous envelope, varying in consistence from a simple flexible membrane to a thick calcareous shell, either solid or porous. He does not, however, regard the differences in the texture of the envelope as equal in importance to those presented by the form of the pseudopodian extensions of the sarcode-body, according to which the Rhizopodes may he divided into two sections; of which the first (corresponding to Ehrenberg's family Arcellina) includes only the Arcellæ and Difflugiæ, whose pseudopodia are short, thick, and rounded at their extremities; whilst the second comprehends all those whose pseudopodia are filiform and much attenuated towards their extremities. This second section was subdivided by Dujardin into three tribes; the first composed of the genera Trinema, Euglypha, and Gromia (all discovered by himself), which are distinguished from Difflugia only by the attenuation of their pseudopodia; the second is composed of the single genus Miliola, which agrees with the ordinary Foraminifera in the possession of a calcareous shell, whilst it corresponds with Gromia in having but a single large aperture from which the pseudopodia extend themselves; and the third includes the Foraminifera proper, all of which were supposed by Dujardin to be furnished (like the few observed by himself) with porous shells for the passage of pseudopodia from the general surface of the body.

Now this arrangement, imperfect though it was, is based (as it