In the Linnæan arrangement, the Anomia form a very comprehensive genus, and since in particular the fossil species are included it should certainly have been divided into several distinct sections or families in order to embrace the different tribes of those shells, which according to the character Linnæus has given of the genus must necessarily be referred to it. It is impossible without some modification of this kind to reconcile _Anomia Ephippium and Cepa_, with _Anomia Caput Serpentinus_ or _Terebratula_, or either of them with _A. Placenta_; and there are besides these some other families which do not well accord, and which might perhaps be separated into distinct genera with great advantage, the fossil kinds especially, which are very numerous and much diversified in structure. It cannot be very material whether they be so divided into genera or be placed in different families under the general appellation of Anomiæ: they are obviously very dissimilar and should be kept apart, and we have examples of both these modes of classing the Anomiæ among the early Naturalists. A late french writer, M. Bosc, speaking of this tribe of shells, observes, that Linnæus having confounded the _Terebratules_ with the _Anomies_, Bruguière first established their differences, and Lamarck had fixed their characters. This observation is not sufficiently explicit, and may possibly imply more than the author of it has intended. It assumes as a conclusion that Linnæus committed an error in confounding these two genera, without informing us in what state of arrangement Linnæus found them. It may be inferred from this that they had been more accurately discriminated before his time, or on the contrary, that they never had been classed in any form, and that it was the want of knowledge in Linnæus which led him to confound shells together that were generically distinct. But whichever we are to understand, the conclusion is, that Linnæus had confounded them, and that it remained for Bruguière and Lamarck to reform those errors of Linnæus, which all later Naturalists had left uncorrected, if not unobserved. Now really this view of the subject is not fairly taken if such an inference be intended. The result of a very little enquiry among the authors who preceded Linnæus, or were immediately subsequent to him, will assure us of the truth of this; and will convince us beyond a doubt, that the discrimination of neither of those authors was necessary either to furnish the Naturalists of the present day with the term Terebratula; to determine the differences that exist between them and the Anomiæ, or to fix the characters by which the Terebratulæ are distinguished.