568 RAMSAY H. TRAQVJA1R ON AMBLYPTERUS, 



sur toute la surface des os qui les portent." G. asper (Palceoniscus 

 DunJceri, Germar) is now referred to the genus Acrolepis ; but another 

 species, G. giganteus, is added from the Old Red Sandstone of Scot- 

 land. Finally, in the general list of Ganoids from the various 

 formations published in 1843, and appended to the beginning of 

 the second volume, G. Ranlinei, from the Coal-measures of Leeds, 

 is named though not described, and G. giganteus is transferred to 

 the genus Holopty chins. The latter is described in the ' Poissons 

 fossiles du vieux Gres Rouge ' (1844), p. 73. 



Another species of Gyrolepis, from the German Muschelkalk, 

 was described hy Minister 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, Miinst., 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. ATbertii 

 and biplicatus as Colobodus varians, Giebel *, and in like manner 

 the species G. tenuistriatvs and maximus as Amblypterus decipiens, 

 Giebel t, 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 J. 



Quenstedt, in his ' Handbuch der Petref actenkunde/ 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, 



* Fauna der Vorwelt, i. 3, pp. 181, 182. 



t Ibid. p. 255. 



\ ' Ueber die Fauna des bunten Sandsteins and des Muschelkalks in 

 Oberschlesien,' p. 67. I have not myself seen this work, which I therefore 

 quote on the authority of Dr. Martin. 



§ Handbuch der Petrefactenkunde, 2nd ed. (1867), pp. 248-250. 



|| Ibid. p. 268, 269. 



