JOHAN KJ^ER. [SEC. ARCT. EXP. FRAM 



very striking description of the inner structure, but strangely enough 

 formed the conclusion, -- although not without some doubt, -- that 

 these remains represent fin spines and fulcra of Asterolepis, Ihe plates 

 of which, however, have quite another structure. ZITTEL, in his 

 Handbuch, Vol. fill, 1887, p. 155 shares the same views. 



S. WOODWARD in his excellent work, "Catalogue of Fossil Fishes", 

 (Vol. I. 1891, pag. 126) places these remains as Ichthi/odorulites and says 

 that in their characters they are nearest Oracanthus. These views are 

 maintained also in his "Outlines of Vertebrate Palaeontology", (1898, p. 29). 



In the same year. R. H. TRAQUAIR in his "Report of Fossil Fishes 

 in the Silurian Rocks of Scotland", which contained so much that was 

 new and fundamental, appeared with quite a fresh interpretation of 

 Psammosteus. By reason of his studies of the most primitive Ostra- 

 codermi and his investigations of the lower Devonian Drepanaspis 

 Gemi'mdenensis, he believed that the fragmentary dermal plates which 

 had been denoted Psammosteus, belong to an ostracoderm fish closely 

 related to Drepanaspis. ,,It is now pretty clear that Psammosteus is 

 closely allied to Drepanaspis, so closely that it may be a question as 

 to whether there is any need for family distinction. I think, however, 

 that it is better for the present to keep them in separate families until 

 the microscopic structure of the hard parts of Drepanaspis can be 

 investigated and more also is known regarding the configuration of 

 Psammosteus and the arrangement of its plates" 1 . 



TRAUUAIR'S description of Psammosteus is so striking and his views 

 appear to be so well founded that the majority of subsequent investiga- 

 tors who have concerned themselves with the systematic position of 

 Psammosteus have subscribed to his hypothesis. In the latest edition 

 of ZITTEL'S Handbuch, E. KOKEN has even arranged Psammosteus under 

 the family Drepanaspidae. 



The present author has succeeded in studying the microscopic 

 structure of Drepanaspis. In this respect he is able to supplement 

 TRAQUAIR'S investigations of this interesting form. It has been found 

 that the structure agrees quite closely with that of Psammosteus, and 

 the agreement is such that the forms must -have been related. This 

 matter will be further discussed later on. 



On the basis of our present knowledge it is easy to decide whether 

 the remains before us are those of a psamrnosteid form. On the other 

 hand it is far more difficult to determine how far we are justified in 



1 Report of fossil fishes in the silurian rocks of Scotland. Trans. Roy. Soc. of 

 Edinburgh, 31, 1898. p. 8*8. 



