JOHAN KLER. 



[SEC. ARCT. EXP. FRAM 



in the skeleton mass. The pulp cavities are generally narrow, canal- 

 like, and are in connection with the underlying vascular canals by means 

 of a narrow opening of the nature of a canal. The denticles are com- 

 posed, as usual, of fine dentine tubules; in the spaces between the 

 denticles we also find intermediary bundles of dentine tubules, that 

 emerge from the underlying canal system and rise amongst the surface 

 denticles. This peculiarity is especially characteristic. In the peripheral 



Fig. 5. Sketch showing the structure of the dermal skeleton of Psammosteus complied- 

 tus new. sp. The dermal skeleton is cut through in several directions. At the top we 

 see the denticles with their pulp cavities and fine dentine tubnles; between them 

 the interim-diary bundles of dentine tubules; and under, the vascular canal system. 



part of the fragment the vascular canals are narrow with thick walls; 

 farther inwards they become wider, but there too the walls are thick 

 with strongly marked dark median layer and lamellar structure. In the 

 longitudinal section we see straight canals, which are sometimes more 

 irregular, and extend in lacunal fashion, often entering into connection 

 with each other by means of large or small orifices and fine canals. 



The fragment described in 1. shows a similar microscopic structure; 

 the vascular canal system, however, is wider in this case, and in the lower 

 part of the plate the latter has thinner walls. 



