88 THE ASTEROLEPIS, 



bercles a deeply tatooed line, c, there occurs what seems to 

 bo a socket, regarding the use of which I am unable to form 



Fig. 42. 



NON-DESCRIPT LATERO-HYOIDAL PLATE OF ASTEROLEPIS. 



(One-third nat. size.) 



a conjecture. There are, besides, certain difficulties which 

 the structure of this portion of the Aster olepis raises, that I 

 am at present unable to lay ; but I can at least record the 

 evidence slowly and hesitatingly rendered by the rocks re- 

 garding it, though I cannot in every case comprehend, as a 

 whole, the meaning which that evidence bears. 



That suite of shoulder-bones that in the osseous fishes forms 

 the belt or frame on which the opercules rest, and furnishes 

 the base of the pectorals, was represented in the Asterolepis, 

 as in the sturgeon, by a ring of strong osseous plates, which, 

 in one of the two species of which trace is to be found among 

 the rocks of Thurso, were curiously fretted on their external 

 surfaces, and in the other species comparatively smooth. The 

 largest, or coracoidian plate of the ring, as it occurs in the 

 more ornate species (fig. 43), might be readily enough mis- 

 taken, when seen with only its surface exposed, for the ich- 

 thyodorulite of some large fish, allied, mayhap, to the Gyr- 

 acanthus formosus of the Coal Measures ; but when detached 



