1897] TAXONOMIC POSITION OF PTERASPIDAE, ETC. 47 



the nostril. If these fishes possessed a nostril, single or double (as 

 presumably they did), it seems that it was placed in such a position 

 as to avoid perforating the bony shields of the head. To assume — in 

 the total absence of evidence pro or con — that these fishes were 

 monorrhine, is surely illegitimate and arbitrary. Further, there 

 are in Eal,craspis and some other head-shields indications of lateral 

 chambers, remotely suggesting lateral branchial chambers ; but the 

 form and position of these would be equally consistent with 

 elasmobranch as with marsipobranch affinities. 



It seems to me that even Huxley's cautious statement as to the 

 affinities of Ptcraspis and Cephalaspis goes too far. He says 

 (Quart. Journ. Gcol. Soc, vol. xiv., p. 279), " A careful consideration 

 of the facts, then, seems to me to prove only the necessity of sus- 

 pending one's judgment." So far I entirely agree with him. He 

 proceeds, " That Cephalaspis and Pteraspis are either ganoids or 

 teleosteans appears certain, but to which of these orders they 

 belong there is no evidence to show." That was written a long 

 time ago. It seems to me that whilst there is abundant evidence 

 to shew that Pteraspids and Cephalaspids, and also Pterichthyids were 

 craniate vertebrates, there is nothing to show conclusively that they 

 are referable to any known group of fishes, rather than that they 

 are to be regarded as representatives of isolated extinct lines of 

 descent. Their possession of paired orbits, fish-like scales, and fish- 

 like median fins, renders it the course involving least assumption con- 

 cerning matters of which we are ignorant, to treat them as detached 

 groups of primitive fish-like forms, concerning the closer relation- 

 ships of which judgment must be suspended. 



The palaeontologist is, we must admit, entitled to make sug- 

 gestions and guesses as to the affinities of the organisms which have 

 left behind them the fragments with which he has to deal. On 

 the other hand, if he aspires to be a zoological taxonomist he must 

 accept the common point of view of zoologists. He does injury 

 rather than benefit to zoological science when (as is, unfortunately, 

 sometimes the case) he endeavours to impose an unwarranted 

 " gness " upon zoological taxonomy as though it were a soberly 

 worked-out conclusion, or reconstructs classifications hitherto based 

 upon the consideration of comprehensive anatomical data, in order 

 to give unnatural prominence to such characteristics alone as are 

 furnished by the hard parts of organisms — parts with which a 

 study of fossil forms renders him specially familiar. 



E. Kay Lankester. 



