Contribution to Knowledge of Paleeospondylus Gunni, 319 
of lingual apparatus. It is hard to imagine the absence of 
the latter in the living state, so that its elements were 
probably composed of a more perishable material; and here 
it may be noted that, in the recent Marsipobranchs, two 
kinds of cartilage enter into the formation of the cranio- 
facial apparatus, of which one is considerably harder and 
more solid than the other In Myzine the hard cartilage 
prevails in the cranium, while the soft variety enters largely 
into the structure of the hyo-lingual parts. A similar 
condition may have existed in Palwospondylus, the hard 
cartilage becoming, in addition, actually calcified, and in this 
way capable of preservation in a schist like that of Achan- 
arras, while the soft utterly disappeared. 
The development, in the sheath of the notochord, of ring- 
like calcified vertebral centra is no bar to the acceptation of 
the Marsipobranch theory. For in this respect the greatest 
differences exist in fishes, both recent and extinct, which 
undoubtedly belong to the same “subclass.” The Paleozoic 
Elasmobranchs were mostly notochordal, so was the Mesozoic 
Hybodus, so is the recent Notidanus, but the Carboniferous 
Chondrenchelys had ring-vertebree, and such modern sharks 
as Lamna, etc., have the centra highly-developed, astero- 
spondylic, biconcave, and calcified. And if the recent 
Marsipobranchs are, as some suppose, degenerate forms, there 
is no reason why a Palzozoic representative of the group 
should not have had differentiated vertebrae, and these, as 
well as the cranium, also calcified. Here I may refer the 
reader to the remarks quoted from Messrs Howes and Smith 
Woodward at the commencement of my former paper on 
Paleospondylus (5, pp. 87, 88; 3, pp. 143, 144; 4, p. 599). 
I have now given the facts of the structure of Palo- 
spondylus so far as the specimens before me permit, and if 
my interpretation of the parts exhibited is correct, there 
seems no escape from the conclusion that the little creature 
must be classed as a Marsipobranch. The subject is not yet, 
however, exhausted; the upper surface of the skull, for 
instance, remains to be described, but again I may express 
1 W. K. Parker, On the Skeleton of the Marsipobranch Fishes—Phil, 
Trans., 1883, part ii., pp. 373-457, 
