232 
DAVIS : DISTRIBUTION OF FOSSIL FISHES. 
The fish of the coal measures have been hitherto regarded as be- 
longing to either the Elasmobranchs or the Ganoids. In recent 
sharks the whole of the framework of the body is frequently cart- 
ilaginous : the vertebrae, the brain -case, and jaws are all composed 
of cartilage. The teeth , the dermal tubercles or shagreen, and, when 
present, the spines protecting the dorsal or pectoral fins, are the 
only parts of the fish which are composed of bone, and, as would 
naturally be inferred, they are the only parts of these fish which 
are found fossil, all the remaining cartilaginous and soft parts have 
been decomposed and lost. Nor is this the only difficulty, the cart- 
ilaginous framework which held the teeth and spines together being 
removed, the latter became separated, and now there are few in- 
stances where the teeth and other fossil parts of the fish can be 
correlated. It is an extremely rare occurrence to find the spines, 
teeth, or dermal shagreen in such relationship with each other, that 
it can be clearly demonstrated that they belong to the same species, 
or even the same genus of fish. The organs on which modern 
classification is based, viz. — the dilated aorta or bidbus arteriosus. 
with its variable series of valvular openings ; the non-decussating 
optic nerves; the spiral valve in the intestine, all serve to dis- 
tinguish the sharks and the ganoids from other fishes at present 
existing. In the fossil fish of the coal measures, the heart, brain, 
and intestines have now no existence, and we can only reason by 
analogy, that as in recent fish we find certain functional relations 
existing between the soft and hard parts of the fishes, so in the 
fossils, having found the hard bony parts preserved, and these ex- 
hibiting certain close relationships with the recent forms, it is 
inferred that the soft and decayed portion of the fish have also 
borne a similar relationship to the recent lorms. 
The Ganoids are more numerous in the coal measures than 
the sharks. Their remains are found in better preservation, their 
bodies being covered with a dense bony envelope of shining scales 
of ganoine, and the internal framework being in most instances 
more or less ossified, the fossils are generally discovered in a toler- 
ably perfect condition. In recent forms the ganoids exhibit in 
