502 MULLER ON THE STRUCTURE OF THE GANOIDS, 
Sturgeons, and in the Sharks. M. Agassiz designates these 
as Heterocerci. In many Ganoids, the extremity of the ver- 
tebral column extends only as far as the commencement of 
the upper tail-piece, it then has superior fin-rays, as in many 
living osseous fishes of the Salmon tribe, Clupea, &c. In other 
Ganoids the vertebral column divides the caudal fin into two 
equal segments, as in most of the osseous fishes; these are the 
Homocerci. 
In a large number of Ganoid genera the fins are remarkable, 
from their anterior margin or first ray being furnished with 
prickly scales, fulcra; others have no traces of them. This dif- 
ference is also marked in the living genera; for Lepisosteus pos- - 
sesses this structure, Polypterus does not. The fulcra princi- 
pally cover that part of the anterior margin of the fin which lies 
free; but where the rays increase in length and appear behind 
one another at the anterior margin, the fulcra pass over their 
extremities from the shorter to the longer rays. In general, the 
Ganoids are related to the Abdominal Malacopterygians in the 
structure of the fins and in the position of the abdominal fins. 
The characters of the orders have been taken by Agassiz from 
the scales, which are mostly angular, rhomboidal, or polygonal, 
and covered with enamel. He enumerates in his large work, 
Recherches sur les Poissons Fossiles, the families Lepidoidei, 
Ag.; Sauroidei, Ag.; Pycnodontes, Ag.; Celacanthi, Ag.; Scle- 
rodermi, Cuv.; Gymnodontes, Cuy.; Lophobranchii, Cuy.; and 
remarks, that after these families, in the order of Ganoids, some 
orders of living fishes must be arranged, as the Goniodontes, 
Siluroidet and Acipenseride. Agassiz has recently added the 
Lepidosiren to the Ganoids. 
We cannot expect, when we consider the slight assistance 
fossils render us, that the families should be separated by such 
marked distinctions as in living animals. The differences be- 
tween the Lepidoidei and Sauroidei are really very slight. Thus 
the former have either sickle-shaped teeth in many rows, or 
they are blunt; the Sauroidei, in which Lepisosteus and Poly- 
pterus are included, have conical pointed teeth, among which 
smaller teeth sometimes occur. The difference in the form also, 
which in the Sauroids is somewhat more elongated, is, after all, 
not material, as we see in the natural families at present in 
existence, such as the Characini and Scomberoidei. Although 
the separation of these two families is merely artificial, still, as it 
