Palichthyologic Notes. No.4—On the Affinities of the Genera Tetragonolepis and Dapedius

Abstract

Before entering upon the descriptions of the many new species of fossil fishes which have accrued to the subfamily Lepidoidei homocerci since the publication of the ‘Poissons Fossiles’ it will be necessary to consider the affinities of the genera Tetragonolepis and Dapedius , arranged by Prof. Agassiz at the head of this subfamily, with reference both to the relations they have to each other, and to the family in which they are placed. Both these genera are adopted by Agassiz, the former from Prof. Bronn, the latter from Sir Henry de la Beche, but (although impressed with the conviction of the existence of the two types) the Professor found the greatest difficulty in defining the demarcation between them, and assigning to each its own generic attributes. Bronn's genus contained but one species, and that a unique specimen from the Lias of Neidingen, in the cabinet of Baron Althaus at Durheim, while Dapedius comprised all the fossil fishes discovered in England that had any resemblance to the figure of Dapedius politus published in the Geological Transactions. Among the latter he found that some had the crowns of the teeth single, while in others they were more or less notched, and he seized upon this as the criterion between the genera, ranking all the single-toothed species with Tetragonolepis and the remainder with Dapedius . All the previously assigned differential features having failed, he adopts this as “le seul caractere constant qui les distingue*.” In the absence of this distinctive character, it is impossible to