48 Fossil Fishes. 



long to a gigantic species of Gyrolepis. Thus the old red-sandstone 

 contains debris of many species of Cephalaspis, of a species of Uip- 

 terus, and of a species of Gyrolepis, (consequently of those genera 

 which belong to the order Ganoides), and many species of Ichthyo- 

 dorulites, which are the bony rays of different fishes of the order 

 Placoides. These bony rays present such remarkable differences, 

 that it is impossible to suppose that they have belonged to the same 

 genus, any more than to any genus, the rays of which are found in 

 the superior geological formations. I shall describe some under the 

 denomination of Ctenacanthus ornatus, and others under that of 

 Onchus JSlurchisoni and Onchus erectus. 



" In descending further into the greywacke group, the debris, of 

 fossil fishes are still to be found at different depths ; and as the re- 

 searches of Mr. Murchison have led him anew to subdivide this se- 

 ries of deposits into many formations, I deem it expedient yet fur- 

 ther to point out in this place the limits, of his subdivision, in order 

 that we may accurately define the layer of the crust of the globe 

 which incloses the first traces of the presence of fishes. 



" Immediately under the old red-sandstone we find the upper por- 

 tion of the superior greywacke series, which Mr. Murchison calls the 

 Ludlow rock, and regards as the first formation of his series. This 

 system is characterized in its upper subdivision, which Mr. Murchi- 

 son designates the Upper Ludlow rocks, by a new species of Avicula, 

 and by the Avicula retrojiexa of Hisinger, by the species of Alrypa, 

 a new species of Cypricardia, the Homonolotus Knighiii (a new 

 genus of Konig), the Leptana lata of Buch, by many new species 

 of Orthis, two new species of Orbicula, different new species of Or- 

 thocera two of Pleurotomaria, a new species of Turbo and Gigantic 

 serpulece. These fossils, which will be described and figured in the 

 work now preparing by Mr. Murchison, are contained in a slightly 

 micaceous, grey-colored, thin-bedded sandstone. The environs of 

 Ludlow Castle, in Shropshire, and those of Croft Castle in Hereford- 

 shire, the western flanks of the Malvern and Abberly Hills in Wor- 

 cestershire, the western slopes of May-Hill, Pain Castle, in Radnor- 

 shire, and the Tewerne Hills, belong to this subdivision. In its cen-^ 

 tral subdivision, the Ludlow rock formation comprehends the Aymes- 

 try and Sedgley limestone, subcrystalline, grey and blue argillaceous 

 limestone, characterized by the Pentamerus Knighiii Sow., the 

 Pileopsis vetusta. Sow., a new species of Bellophon, a species of 

 Lingula one of Atrypa, the Terebratula Wilsoni Sow., the Cklw 



