CLASSIFICATION OF DEVONIAN FISHES. 



29 



5. The Teleostei have hitherto been supposed to be entirely 

 absent from formations of Palseozoic age, and no doubt they do not 

 exist under those forms which are most familiar to ichthyologists 

 acquainted with marine fishes, or with the fresh-water fishes of 

 temperate climates ; but, nevertheless, I shall now endeavour to 

 show that there are grounds for something more than a suspension 

 of judgment, as to the vahdity of the ordinary doctrines held upon 

 this subject. 



The remarkable genera Goccosteus and Pterichthys are those 

 which, among all Devonian fishes, have been by common consent 

 regarded as the most heteroclite and anomalous, some writers 

 having gone so far, in fact, as to imagine that these hard cased 

 vertebrates offered us a transition to the shelled Invertebrata. 



Nevertheless, I trust I shall be able to show that the one of 

 these two closely allied genera — Goccosteus — is best, indeed, I may 

 say only, to be understood, by comparing its bony shields with 

 those which cover the roof of the cranium and the anterior part 

 of the body of certain existing Siluroid Teleosteans. 



To this end, however, I must first give the conception of the 

 structure of Goccosteus which my own investigations, guided by 

 those of my predecessors Agassiz, Miller, EgertoD, and Pander,* 

 have led me to form. 



The superior wall of the skull only, seems to have been ossified in 

 this fish, and forms a great shield, which may be roughly said to 

 have a hexagonal figure. The posterior and posterolateral sides of 

 the hexagon are pretty nearly straight lines, while the anterior side 

 is rounded off", to form the snout, and the antero-lateral sides, the 

 longest of all, have their anterior moieties deeply excavated, to 

 constitute the upper part of the walls of the orbit. From before 

 backwards, in the median line, the contour of the cranial shield is 

 nearly straight, but from side to side it is convex, in consequence, 

 more particularly, of the downward inflexion of its postero-lateral 

 angles. The sutures, which separate the various constituent bones 

 of the skull, may readily be confounded with certain superficial 

 grooves of a totally different import, but, by grinding away the 

 outermost layer of bone, this source of error is avoided ; and it 

 is then seen that the cranial sutures have the arrangement repre- 

 sented in the woodcut, fig. 19, and define the several bones from 

 one another with great sharpness. 



* Compare Agassiz, " Monog. des Poissons Fossiles du Vieux Gres Kouge ; " 

 H. Miller, " Old Red Sandstone " and Quart. Jour. Geol. Soc. 1859; Pander, "Ueber 

 die Placodermen des Devonischen Systems, 1857;" Sir P. Egerton, "Remarks on the 

 Nomenclature of the Devonian Fishes," Quart. Jour. Geol. Soc. 1859. 



