ITS STRUCTURE, BULK, AND ASPECT. 89 



from the stone, the hollow form and peculiar striae of the in- 

 terior surface serve to establish its true character as a dermal 

 Fig. 43. 



P SHOULDER {i. e. CORACOID ?) PLATE OF ASTEROLEPIS. 



(One-third nat. size, linear.) 



plata The diagonal furrowings which traversed it, as the 

 twisted flutings traverse a Gothic column moulded after the 

 type of the Apprentice Pillar in Koslin Chapel, seem to have 

 underlaid the edge of the opercule ; at least I find a similar 

 arrangement in the shoulder-plates of a large species of Dip- 

 lopterus, which are deeply grooved and furrowed where the 

 opercule rested, as if with the design of keeping up a com- 

 munication between the branchiae and the external element, 

 even when the gill-cover was pressed closely down upon them. 

 And, — as in these shoulder-plates of the Diplopterus the fur- 

 rows yield their place beyond the edge of the opercule to the 

 punctulated enamel common to the outer surface of all the 

 creature's external plates and scales, — we find them yielding 

 their place in the shoulder-plates of the Asterolepis to the 

 starred tubercles. 



A few detached bones, that bear on their outer surfaces 

 the dermal markings, must have belonged to that angular- 

 shaped portion of the head which intervened between the 

 cranial buckler and the intermaxillary bone ; but the key 

 for assigning to them their proper place is still to find '; and 

 I suspect that no amount of skill on the part of the compa- 

 rative anatomist will ever qualify him to complete the work 

 of restoration without it. I have submitted to the reader 

 the cranial bucklers oifive several genera of the ganoids of 

 the Old Red Sandstone ; but no amount of study bestowed 



