102 TRANSACTIONS OF THE [san. 13, 
sive from the evidence of this single fossil. But their presence 
is alone sufficient to cause us to review with some care the 
interpretations which have already been put upon the struc- 
tures of the head and gill region of the fossil. .Thus it is 
evident that if ray-like structures are present on the side of the 
body as far forward as the anterior end of the post-occipital 
plates, the ‘“ enlarged posterior part of the skull,” which Dr. 
Traquair regards as “ presumably composed of the combined 
parachordals and ear capsules,” can no longer be looked upon 
as strictly a cranial region, but was rather the encasement of 
the branchial apparatus. And it would naturally follow that 
the capsules of the ear and eye would have to be sought in a more 
anterior situation, in the positions, perhaps, indicated in Tra- 
quair’s figures in the “trabeculo-palatine part of the cranium ” as 
a,borc. The evidence that the ray-like structures were associated 
with lateral, rather than with vertical fins (as the present 
writer at first supposed) is by no means unsatisfactory. (1) 
The head and post-occipital plates of the fossil are arranged 
in perfect bilateral symmetry, showing that there was no 
torsion of these regions during petrifaction. (2) The ray-like 
structures of either side corrrespond to each other, and in their 
extreme anterior position find no analogue among the unpaired 
fins of existing fishes, even among the aberrent Heterosomes and 
Fierasfer. Negative as well as positive evidence, accordingly, 
indicates that these fin-like rays were concerned with the pres- 
ence of paired fins. If this be true, is Paleeospondylus to be re- 
garded as a Marsipobranch? It is certain that the appearance 
of these fin-like structures must give weight to those characters 
of the fossil which have been adverse to its cyclostomian affini- 
ties, and must also tend to make more prominent the lack of 
precise knowledge as to its Myxinoid features. The evidence, 
favorable and unfavorable, might perhaps be summarized thus: 
