342 M. Agassiz on Fishes. 



by Professor Jameson and Mr Lyell. Lastly, the scales of the old 

 red-sandstone of Fifeshire, which have been described by Dr Flem- 

 ing, belong to a gigantic species of Gyrolepis. Thus the old red- 

 sandstone contains debris of many species of Cephalaspis, of a species 

 of Dipterus, and of a species of Gyrolepis, (consequently of those 

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

 Ichthyodorulites, 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 Ctenacanlhus ornatus, and others under that of 

 Onchus Murchisoni and One hits 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 series 

 of deposits into many formations, I deem it expedient yet further to 

 point out in this place the limits of his subdivisions, in order that we 

 may accurately define the layer of the crust of the globe which in- 

 closes 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 Murchison 

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

 by the Avicula retroflexa of Hisinger, by a new species of Atrypa, a 

 new species of Cypricardia, the Homo/iolotus Knightii (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 Orthocera, two 

 of Pleurolomaria, a new species of Turbo and 'Gigantic serpulce. 

 These fossils, which will be described and figured in the work now 

 preparing by Mr Murchison, are contained in a slightly micaceous, 

 grey-coloured, thin-bedded sandstone. The environs of Ludlow 

 Castle, in Shropshire, and those of Croft Castle in Herefordshire, 

 the western flanks of the Malvern and Abberly Hills in Worcester- 

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

 shire, and the Trewerne Hills, belong to this subdivision. In its 

 central subdivision, the Ludlow-rock formation comprehends the 

 Aymestry and Sedgley limestone, subcrystalline, grey and blue ar- 

 gillaceous limestone, characterized by the Pentamerus Knightii, Sow., 

 the Pileopsis vetusta, Sow., a new species of Bellerophon, a species 

 of Lingula, one of Atrypa, the Terebratula Wilsoni, Sow., the Cala- 

 mopora fibrosa, Goldf., and some other corals. This subdivision is 

 remarkably well developed near Aymestry in Herefordshire, in some 

 parts of Shropshire, and at Sedgley in Staffordshire. The third 

 and last subdivision is that of the lower Ludlow rocks ; these are 

 concretionary and sandy limestones, and sandy shales of a dark colour ; 

 and are especially developed in the escarpments of Monktree and 

 Bridgwood in the valley of Woolhope in Herefordshire, in the escarp- 

 ments in Montgomery and the Radnor Forest ; and are characterized 

 by three species of Phragmoceras (a new genus of Mr Broderip), by 

 the Asaphus candatus, Brogn. ; two species of Cardiola (new genus of 

 Brod.), a new species of Nautilus, two of Spiraliies, a Pentamerus, 



