THE UPPER SILFRIAjNT OE NORTH AMERICA. 49 



The reference of these spines to Selachians or Siluroids may 

 prove unfounded, and it is quite possible that when we know all 

 the details concerning the fossils next mentioned, the two may 

 prove to belong to the same species. 



It is right to remark here that some of these fossil spines from 

 the English Ludlow rocks have been regarded by some geologists 

 as of Crustacean origin. However this may be, the Pennsylvanian 

 specimens show no such affinity, but in their rounded flutings much 

 more closely resemble genuine fin-spines or ichthyodorulites. 



The second and more abundant kind of these Ludlow fossils, 

 though now, by general consent, admitted to the class of fishes, is 

 so strange in form and structure, and so aberrant from the usual 

 type, that its right to that rank has been doubted and denied. The 

 sj)ecimen8 are oval, thin shields or plates, folded in at the sides, and 

 with a curved surface. They measure only a few inches in length, 

 and formed the cephalothoracic covering of the animal, the rest of 

 whose body was soft and unprotected, or, at most, only covered with 

 scales. 



The study of these peculiar forms has been undertaken by Professors 

 Huxley and Pay Lankester. The former has published his results 

 in the Journal of the Geological Society (1858), and the latter in 

 the Memoirs of the Palaeontographical Society (1867 and 1869). 

 The former has dealt chiefly with the microscopic structure, and the 

 latter with the outward form. 



Postponing for the present further detail on this point, I will 

 only remark that I have no intention here of asserting or defending 

 the claim of these Ludlow fossils to the name of fishes. The authors 

 just cited have done this in no uncertain manner. 



Says the former, " Leaving Prof. Pander's ' Conodonts ' out of the 

 question, Cephalaspis and Pteraspis are among the oldest, if they 

 are not the very oldest, of known fishes." 



Again, "No one can, I think, hesitate in placing Pteraspis 

 among fishes. So far from having no parallel among fishes, it 

 has absolutely no parallel in any other division of the animal 

 kingdom " *. 



If any doubt remained in regard to the zoological position of 

 these fossils, it has since been removed by the finding of a single 

 specimen showing a few scales attached to the matrix behind the 

 cephalothoracic shield. This unique and invaluable specimen has 

 been figured by Professor Lankester in his monograph. 



Assuming, therefore, as proved, the ichthyic nature of these 

 English Silurian fossils, I propose in the first place to offer proof 

 that the Pennsylvanian specimens belong to the same family as the 

 Ludlow Pteraspis, and, in the second, to show that the strata in 

 which they occur are as low as any which have hitherto yielded 

 fish-remains in any part of the world. 



* Though Prof. Huxley's opinion is perfectly obvious, yet the meaning of 

 this expression is doubtful. It is true that the structure in question has no 

 parallel in any other division of the animal kingdom, but it is equally true, as 

 will appear later, that it has no parallel among fishes, 



Q.J.G.S. N0.I6L E 



