1898-1902. No. 33.] UPPER DEVONIAN FISH REMAINS. 



35 



These assumptions of PANDER are mainly of historic interest as far 

 as we are concerned. After TRAQUAIR'S investigations, which have been 

 carried further by my own proofs of the structure of the skeleton, it has 

 been considered certain that Psammosteus, Drepanaspis and Pteraspis 

 are nearly related forms. Drepanaspis, the dermal skeleton of which is 

 known in most details, should therefore provide us in the main with a 

 representation of the appearance of Psammosteus as well. 



In this connection, however, it is of great interest to note that the 

 Psammosteus remains in the East Provinces of Russia according to 



Fig. 8. Sketch showing the structure of the dermal skeleton of Psammosteus maean- 



<lrinus AG. We see the dermal skeleton cut through in two directions. At the 



top, the flattened denticles with their fine, narrow pulp cavities and fine dentine 



tubules; below these the vascular canal system. 



PANDER'S theory belong to one species, which would in that case receive 

 the name Ps. maeandrinus Ac. 



A. SMITH- WOODWARD in his catalogue 1 names AGASSIZ'S species 

 without giving his reasons for so doing. 



In reality a fresh investigation is required, - particularly of the 

 microscopic structure - in order to decide this question. 



Personally I have only had a few Psammosteus remains from the 

 Baltic Provinces for comparison, viz. a spine shaped element from the 



1 Catalogue of the Fossil Fishes in the British Museum, II, 1891, page 126. 



