January 25, 1900J 



NA rURE 



307 



SOME RECENTLY DISCOVERED SILURIAN 

 FISH REMAINS. A LINK IN THE CHAIN 

 OF ORGANIC EVOLUTION} 



rj'VER since the days of Agassiz and Murchison the subject 

 ^^ of the Lower Pali\;ozoic Fish Fauna has been the most 

 sensational in the department of Pakvichthyology, mainly on 

 iccount of the existence at that early period of forms known as 

 Cephalaspidian and Pteraspidian (Osteostraci and Heterostraci 

 if recent classifications), so strangely constituted as to be well- 

 nigh irreconcilable with any of our recent and more familiar 

 fishes. Analogy to certain living species (ex. Coffer Fishes) 

 seemed to suggest that, though archaic, these forms are 

 among the most specialised of all known fishes, and while there 

 has been a general consensus of opinion that this may be so, 

 recent tendency has gone to regard them as the specialised 



their unique interest. Great though the memoirs of these and 

 other investigators as concerning these strange organisms, none 

 of them, from a point of view of general interest and accuracy 

 of detail, excel those of the author of the two under review, 

 our foremost authority in Palaeozoic Ichthyology. His descrip- 

 tions and restorations of these creatures are everywhere repro- 

 duced, and it is matter for sincere congratulation that he should 

 recently have been compelled to return to their study. 



Most particularly does the above remark apply to the 

 Pteraspidise, with the determination of the systematic position 

 of which the monographs before us are mainly concerned, and 

 the conclusions arrived at are the more welcome, in view of a 

 recent attempt to deduce, from the discovery of supposed 

 resemblances in the minute structure of their plates and the 

 exoskeleton of the King Crabs, a belief in a genetic relation- 

 ship between the two — one of those notoriously flagrant flights 



..;jc. 



Fig. I. — T/ielotiiis Pagei, dorsal aspect, one-third natural 



Fig 2. — Lanarkia s/>inosit, rest'>red out- 

 line, with spines, half natural size. 



representatives of an ancient and primitive stock, believed by 

 some to have been aqnathous, and even akin to the Lampreys 

 and Hags, which in our modern classificatory systems are not 

 admitted to the Class Pisces at all. 



Pander, McCoy and Huxley are among the names of past- 

 masters memorably associated with the record of their early 

 discovery ; and, in later years, Powrie, Lankester, Jaekel, 

 Keis and others ; while Rohon has quite recently made 

 them the subject of far-reaching generalisation in cephalo- 

 genesis, which, though extravagant, has sufficed to maintain 



1 " On Thelodus Paget, from the Old Red Sandstone of Forfarshire," and 

 " Report on the Fossil Fishes collected by the Geolog. Survey of Scotland in 

 the Silurian Rocks of the South of Scotland." By R. H Traquair, LL.D., 

 F.R.S., being Nos. 21 and 32 of Part 3, vol. 29, Trans. R. Soc. Edinb. 



NO. 1578, VOL. 61] 



of fancy which during recent years have done so much to bring 

 pure morphology into unjust ridicule. Needless it is to say that 

 the author of the memoirs dismisses this as unfounded. 



Conspicuous among Dr. Traquair's later papers on these 

 remarkable forms is that describing (Proc. Roy. Phil. Soc. Kd., 

 vol. xii,)agiant Cephalaspis (C maxyHiJica) ixom the Old Red 

 Sandstone of Caithness. At the time of its appearance (Dec. 1893) 

 it seemed to those interested to give promise of further unique 

 material from the Scottish Palaeozoic ; and, sure enough, in his 

 penultimate discourse as Swiney Lecturer, the author, on 

 October 12, 1898, announced at South Kensington the dis- 

 covery of the remains here under consideration. At that lecture 

 he dealt fully with the long known Coelolepis scale, and dis- 

 sipated the anomalies which had hitherto beset it, showing it to 



