* * * * * [Sidenote: Latest Systematic Works.] It has been mentioned above that the great work of Cuvier and Valenciennes had been left incomplete. Several authors, therefore, supplied detailed accounts of the orders omitted in that work. _Müller_ and _Henle_ published an account of the Plagiostomes, and _Kaup_ of the Murænidæ and Lophobranchii. _A. Duméril_, finally, commenced an “Histoire naturelle des Poissons ou Ichthyologie générale,” of which, however, two volumes only appeared, containing a complete account of the “Plagiostomes” (Paris, 1865, 8vo.), and of the “Ganoids and Lophobranchs.” (Paris, 1870, 8vo.) So great an activity had prevailed in Ichthyology since the publication of the “Histoire naturelle” by Cuvier and Valenciennes, and the results of the manifold enquiries were scattered over such a multitude of publications, that it became imperative to collect again all these materials in one comprehensive work. This was done in the “Catalogue of Fishes,” published by the Trustees of the British Museum, in eight volumes (Lond. 1859-70). Beside the species previously described many new forms were added, the number total of species referred to in those volumes amounting to 8525. As regards the systematic arrangement--Müller’s system was adopted in the main, but the definition of the families is much modified. This, however, need not be further entered into here, and will become sufficiently apparent in the subsequent parts of the present work. [Illustration: Fig. 1.--Lower aspect of head of _Raia lemprieri_.] CHAPTER II. TOPOGRAPHICAL DESCRIPTION OF THE EXTERNAL PARTS OF FISHES. [Sidenote: Form of the body.]