President's Address. 379. 



armature than a set of eight slender geniculated ossicles 

 on each side behind the head. These two genera he 

 places in his order of Anaspida. According to the view 

 of Dr Traquair, this find of Fossil Fishes which he has 

 described is of very great morphological significance. The 

 order of the Heterostraci, made to hold the Pteraspidae, must 

 also include the Coelolepidse, the Psammosteidse, and the 

 Drepanaspidse. He considers that, beginning with the 

 Coelolepidae, with shagreen-like plates or spines, there is 

 a progressive specialisation of the dermal armour through 

 the Psammosteidse to the Pteraspidae, in which there is 

 a carapace with solid plates. From their shagreen-like 

 armour, he thinks that the Ccelolepidae were probably- 

 derived from some primitive form of Elasmobranch ; but 

 of that he is not certain. He also considers that Ateleaspis 

 above-mentioned shows a connection between the Hetero- 

 straci and the Osteostraci. Dr Traqu air's classification is 

 therefore as follows: — Under the subclass Ostracodermi he 

 places the orders Heterostraci, Osteostraci, and Anaspida. 

 As if it were in prophetic anticipation of the above great 

 discoveries, Dr Traquair had already described a species 

 of Psammosteus, P. Taylori, after the finder, Mr Taylor, of 

 Llanbryde, from the Upper Old Eed Sandstone of Moray- 

 shire, as well as the Thelodus (Cephcdoptertcs) Pagei above- 

 mentioned, and had procured for the Museum of Science 

 and Art some very fine specimens of Drepanaspis from 

 the Lower Devonian of the Hunsrtick, in Germany, which 

 placed him in a position the more readily to grasp the 

 significance of his discoveries. 



Part II. 



As already stated, the second part of this address is 

 devoted to showing the bearing of these discoveries in 

 Palsentology during the last twenty years on the geology 

 of Scotland. For this purpose I shall consider the geolog- 

 ical formations in the order of their relative antiquity, 

 beginning with the most ancient and proceeding towards 

 the younger. 



