• -^ - '-""^ ^°:33 ] ^^UPPERJ^EVONIA^-'ISH REMAINS. 33 



a-^pect ,VVl' ^ "^''''^^ "^'" absence of a cloacal opening on the aboral 

 Hie oral one'' """".'"'"=^"^«^"t »f "^--^ lail, and its apparent presence on 

 consequenliv' [a ''f'""''"' '" "^ P'"'"*' ""^^ ^^e aboral margin of the tail 

 ,u^ „,.,i ' " "^ entire creature, i s the dorsal aspect. Conversely 

 iiie oral aspect is il i 



, . ' "- central; and my previous orientation of the 



creature is correct n u 



,1 , ., niatter on which side of it the openings supposed 



to be orbits are placed". i^ » ki 



Im my oponion none of these arguments is decisive. As regards 

 the first on, I do n,,( deny that Drepanaspis has had a hetero- 

 cercal caudal fin; but none of the examples depicted by Traquair show 

 how the dorsal lobe of the tall is situated with relation to the charac- 

 teristic plates on the more anterior part of the crealure. In fact only 

 one of the specimens certainly shows this dorsal lobe, (fig. 1, in plate II 

 of his supplement); but none of the plates is here shown so distinctly that 

 it is possible to arrive at a result. With regard to the second argument, 

 that which Traouair takes to be a probable cloacal opening has probably 

 nothing to do with that part. It is simply an arch behind the 

 dorsal shield, caused by the inseition of the dorsal spine 

 at this point. 



In support of this contention I have depicted a specimen of Dre- 

 panaspis belonging to the palaeontological collection of Kristiania 

 University. This shows not only the presence of the dorsal spine referred 

 to, but also other things of importance. 



The specimen shown in approximately half natural size in fig. 7 

 (in the text) shows excellently the caudal end although, unfortunately, 

 not the extreme portion of the caudal fin — and the posterior portion 

 of the body plates. There is no doubt that we here see that side of 

 the creature which Traquair regarded as the ventral. The large median 

 plate shows the characteristic fold the extreme rear of which TRAurAin 

 considered to be the cloacal opening. Behind this opening and juineti 

 to it, however, we see a pointed skeleton element which is broader 

 than the succeeding fulcra and which can hardly be anyllnng but a slioit 

 dorsal spine. Behind this we see a continou? ri.w of fulcra which by 

 degrees grows larger and larger. This in my opinion is the upper 

 margin of the tail. It is clear that the tail has been turned to one side 

 and farthest down to the left, therefore, we observe the --«"^ J'^ 



opposite row of fulcra. As we see, ^'^ ^ ;-:-;^ ':;-1.:^: 

 shaped. If we compare this with Traouaih ^' - -^;;" ^^^ ,^ ^^„^ 



men', PL H, %• 1- i" -^-^;^^^:;r:;r ^ fla on the lower 

 apparer,t, we again find similar long, spme P ^ 



