OF SOUTH CAROLINA. 31 
That at least apparent exceptions should arise in the application of this system, was to be 
expected. The mackerel, for instance, has both ctenoid and cycloid scales, and therefore, at first 
sight, presents one of the strongest cases that can be produced as an objection to this classification ; 
but a closer examination shows that so far from being really an exception, it affords the strongest 
possible proof of its truth and accordance with nature—the mackerel, as shown by its organization, 
being the connecting link between the two orders, and hence is characterised by the scales of both. 
The oldest known fishes, or those found in the lowest rocks, belong to the first order, or Placoids ; 
their remains consist, for the most part, of certain spinous appendages found in the fins, very 
similar to the well known process near the tail of the common ray of the coast, which is called by 
the fishermen the “sting.” These fossils have received the name of Ichthyodorulites. 
In the old red sandstone well characterised entire fishes occur for the first time, but so unlike all 
others of their class that they have been referred to both the Articulata and Chelonia respectively. 
“Never shall I forget,” says Agassiz, “the impression which the sight of these creatures, pro- 
vided with appendages resembling wings, produced upon me when I had assured myself that they 
belonged to the class of fishes. It was an entirely new type, which was about to figure, for the 
first time since it had ceased to exist in the series of beings—again to form a link, which nothing 
that had been revealed up to the time, with regard to extinct creations, would have led us even to 
suspect the existence of; showing forcibly that observation alone can lead us to the recognition of 
the laws of development of organized beings, and how much we should guard against all those 
systems of transformations of species which the imagination invents with as much facility as 
reason refutes.” : 
The Ganoids which make their appearance here include the remarkable group of sauroid fishes 
having an organization approaching that of reptiles. Two genera alone of this group are living— 
one an inhabitant of the Nile and the other the gar or Lepidosteus, of the rivers of America. The 
Sauroid fishes are distinguished by certain peculiarities of the teeth, which are common to Saurians ; 
they are conical, pointed and striated. The Lepidosteus has the air bladder cellular, which shows 
a still nearer approach to the air breathing animals. 
To convey even a distant idea of the strange inhabitants of the deep at this period, without 
figures and minute details, would exceed the limits of what is intended as a mere outline, to be, 
filled up .by the reader at his leisure. The fishes of these two orders, the Placoids and Ganoids, 
continued the sole inhabitants of the seas up to a comparatively recent period in the earth’s 
history. 
The other two orders, the Cienoids and Cycloids, first appear in the cretaceous system where the 
Sauroid family of the Placoids ceased to exist, with the exceptions already mentioned. 
SuB-KINGDOM ARTICULATA. 
The class Crustacea of this sub-kingdom has received some attention from Paleontologists, and 
more especially the family of Trilobites—but the ordinary fossil crustacea, which are not uncom- 
mon in the tertiary formation, have not yet received, in our country, the attention which they 
deserve. We generally find only detached portions of crustacean exuvia, such as the carapace 
and claws, and it is not always easy to refer them with certainty to their living types, supposing 
