30 



JOHAN 



[SEC. ARCT. EXP. FRAM 



of the structure, although of course transformation by pyrites had its 

 unpleasant effects. 



PI. Ill, figs 5 6 are direct photographs of my microscopic sections 

 arid in comparison with the other illustrations of microscopic sections of 

 Psammosteus remains, show a complete agreement with that genus. 

 Fig. 6, (in the text) gives us a more diagrarnatical view of the structure 

 with clearer details. It passes trough both the upper and the lower 

 body plate. The fish has been pressed so strongly in the schists that 



Fig. 0. Sketch showing the structure of the dermal skeleton in Drepanaspis 

 Gemilndenensis, SCHLCTER. The section is made through one of the upper and one 

 of the lower body plates. The latter are so greatly compressed that the inmost 

 layer of the skeleton is crushed. At the extreme top and bottom we see the den- 

 ticles with their wide pulp cavities and fine dentine tubules; below them is the 



vascular canal system. 



both of these plates have pressed against each other and partly crushed 

 in the inner parts. Otherwise in this and in the said plate we see the 

 vascular canal system, with narrow canals and orifices in the upper part 

 and more open ones in the lower. Thus on the upper surface we have 

 the denticles with fine dentine tubules and very wide pulp cavities, 

 which are in connection by means of a broad orifice with the underlying 

 vascular canals. By their characteristic form, these denticles constitute 

 the surface sculpture. This was not very thoroughly described in 

 TRAQUAIR'S works, nor do his illustrations convoy so exact a picture 



