1853.] EGERTON PALiCHTHYOLOGIC NOTES. 275 



toothed species with Tetragonolepis and the remainder with Bapedius. 

 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 determine 

 to which of the two genera any given specimen may belong. For 

 instance, two British species from the Lias of Barrow on Soar, 

 assigned by Agassiz to the Tetragonolepides, are proved by the recent 

 discovery of the teeth to belong to the Dapedii, if the discrimina- 

 tion of the genus turns upon the form of the teeth . But, alas for 

 the constancy of fishes' teeth ! a specimen came into my hands not 

 long ago having a combination of the two forms of tooth, the prin- 

 cipal sets in each jaw being conical and single-pointed, and all the 

 subsidiary teeth bifurcate (Plate XI. fig. 1). Having my attention 

 thus directed to this point, I have since found a specimen of Bapedius 

 imnctatus in Lord Enniskillen's collection which has both forms of 

 tooth in the principal series in both jaws (Plate XI. fig. 2). The 

 conclusion therefore is irresistible, that the form of tooth is a cha- 

 racter too capricious to be relied upon in this instance as a generic 

 definition. 



This much had I written before my arrival in London, and after a 

 careful review of the whole subject had determined to recommend the 

 union of the two genera under Sir Henry de la Beche's title Bapedius, 

 that having the claim of priority over Tetragonolepis. In consequence, 

 however, of the fortunate discovery by the Rev. Mr. Brodie of several 

 specimens of a small fish belonging to this group in the Upper Lias 

 of Gloucestershire, I am now enabled to throw considerable light, not 

 only on the generic but on the systematic relations of these curious 

 ichthyolites, and to advocate the propriety of retaining the genus 

 Tetragonolepis, as being wholly distinct from Bapedius, and belonging 

 most probably to a different family. 



I was struck at first sight with the strong resemblance Mr. Brodie' s 

 fish bore to the original specimen of Tetragonolepis semicinctus, on 

 the examination of which Bronn founded the genus. On referring to 

 the description and figure given by him in the ' Jahrbuch fiir Mine- 

 ralogie,' &c. p. 22, 1830, my opinion was confirmed as to the generic 

 identity, although specific differences were perceptible. In November 

 1841, Count Miinster, in a letter to the editors of the ' Jahrbuch f,' 

 alludes shortly to a small species of Tetragonolepis, from the lias 

 of Wurtemburg, which he at first took for a specimen of Tetragonolepis 

 semicinctus of Bronn, but finding the abdominal scales to be serrated, 

 he named it Tetragonolepis subsei'ratus. Having received from the 

 late Dr. Hartmann of Goppingen several specimens of the latter 

 species, from the lias of Banz and Ohmden, I have been able to 

 make a close comparison between these and Mr. Brodie' s specimens, 

 and find an important character constant in all, in the mode of 

 articulation of the scales, together with other common features of 

 much significance. One of the reasons which induced Prof. Bronn 



* Poissons Fossiles, vol. ii. p. 181. 

 t Jahrbuch fiir Mineralogie, 1842, p. 97. 

 VOL. IX. — PART I. V 



