194 FISHES. 



remains is not rather from Annelids and Mollusks than from 

 Fishes, 



[See G. J. Hinde, in "Quarterly Journal of the Geological Societj^," 1879.] 



The first nndeniable evidence of a fish, or, indeed, of 

 a vertebrate animal, occurs in the Upper Silurian Eocks, in 

 a bone-bed of the Downton sandstone, near Ludlow. It con- 

 sists of compressed, slightly curved, ribbed spines, of less 

 than two inches in length (Onchus) ; of small shagreen-scales 

 (Thelodus) ; the fragment of a jaw-like bar with pluricuspid 

 teeth (Plectrodus) ; the cephalic bucklers of what seems to be 

 a species of Pteraspis ; and, finally, the coprolitic bodies of 

 phosphate and carbonate of lime, including recognisable re- 

 mains of the Mollusks and Crinoids inhabiting the same 

 waters. But no vertebra or other part of the skeleton has 

 been found. The spines and scales seem to have belonged 

 to the same kind of fish, which probably was a Plagiostome. 

 It is quite uncertain whether or not the jaw (if it be the 

 jaw of a fish'') belonged to the buckler-bearing Pteraspis, the 

 position of which among Ganoids, with which it is gener- 

 ally associated, is open to doubt. 



No detached undoubted tooth of a Plagiostome or Ganoid 

 scale has been discovered in the Ludlow deposits : but so 

 much is certain that those earliest remains in Palaeozoic 

 rocks belonged to fishes closely allied to forms occurring in 

 greater abundance in the succeeding formation, the Devonian, 

 where they are associated with undoubted Palseichthyes, 

 Plagiostomes as well as Ganoids. 



These fish-remains of the Devonian or Old Red Sandstone, 

 can be determined with greater certainty. They consist of 

 spmes or the so-called Ichthyodorulitcs, which show sufficiently 

 distinctive characters to be referred to several genera, one of 



■^ Ray Lankester considers it to be a portion of the long denticulated 

 cornua of a genus Eukerasjns allied to CqjJialasjjis. 



