Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/668

568 sur toute la surface des os qui les portent." G. asper (Palæoniscus Dunkeri, Germar) is now referred to the genus Acrolepis; but another species, G. giganteus, is added from the Old Red Sandstone of Scotland. Finally, in the general list of Ganoids from the various formations published in 1843, and appended to the beginning of the second volume, G. Rankinei, from the Coal-measures of Leeds, is named though not described, and G. giganteus is transferred to the genus Holoptychius. The latter is described in the 'Poissons fossiles du vieux Grès Rouge' (1844), p. 73.

Another species of Gyrolepis, from the German Muschelkalk, was described by Münster under the name of G. biplicatus, characterized by the possession of two strong parallel ridges on the outer surface of the scale.

But in 1848 Giebel announced that he had discovered the scales known as Gyrolepis Albertii, Ag., and G. biplicatus, Münst., in great numbers, and on the same slabs with dentigerous and other cephalic bones referable to Colobodus, a genus instituted by Agassiz for certain tooth-bearing fragments (C. Hogardii, Ag.) from the Muschelkalk, and referred by him to the family of Pycnodonts. Gyrolepis tenuistriatus, Ag., on the other hand, was referred by Giebel to Amblypterus. He therefore proposed the total abolition of the genus Gyrolepis, uniting and renaming the species G. Albertii and biplicatus as Colobodus varians, Giebel, and in like manner the species G. tenuistriatus and maximus as Amblypterus decipiens, Giebel , and in each case apparently without the smallest regard to priority of specific nomenclature. The accuracy of Giebel's reference of the two former species to Colobodus was questioned by Eck.

Quenstedt, in his 'Handbuch der Petrefactenkunde.' agrees with Giebel as to the reference of G. Albertii and G. maximus to Colobodus; Tholodus, v. Meyer, he also considers as belonging to the same type, but is inclined to consider these forms as related, not to the Pycnodonts nor to the heterocercal Ganoids, but to Lepidotus. In the same work he expresses himself in a rather guarded manner regarding the reference of G. tenuistriatus to Amblypterus.

The doubtful nature of the characters of Gyrolepis is thus referred to by Sir Philip Grey-Egerton in his paper on the "Ganoidei Heterocerci:"—"The scattered and fragmentary condition in which the remains of this genus have always been found has proved hitherto an insurmountable obstacle, not only to a definition of its generic characters, but to a determination of the family in which it ought to be placed. It is not even known whether the tail was homocerque or heterocerque—a point of some importance as bearing upon the value of this character as a criterion of the age of strata,