1898-1902. No. 33.] UPPER DEVONIAN FISH REMAINS. 33 



Second: - That the absence of a cloacal .opening on the aboral 

 aspect of the commencement of the tail, and its apparent presence on 

 the oral one, is equivalent to a proof that the aboral margin of the tail 

 consequently of the entire creature, i s the dorsal aspect. Conversely 

 the oral aspect is the ventral; and my previous orientation of the 

 creature is correct, no matter on which side of it the openings supposed 

 to be orbits are placed". 



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

 the first on, I do not deny that Drepanaspis has had a hetero- 

 cereal caudal fin; but none of the examples depicted by TRAQUAIR show 

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

 teristic plates on the more anterior part of the creature. 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 TRAQUAIR 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 insertion 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 TRAQUAIR 

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

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

 than the succeeding fulcra and which can hardly be anything but a short 

 dorsal spine. Behind this we see a continous row 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 second and 

 opposite row of fulcra. As we see, this is unusually long and spine 

 shaped. If we compare this with TRAQUAIR'S illustration in his Supple- 

 ment, PI. II, fig. 1. in which the heterocercal nature of the tail is quite 

 apparent, we again find similar long, spine shaped fulcra on the lower 



3 



