1044 
SCANDINAVIAN FISHES. 
only two types survive, inhabitants of the tropical re- 
gions of Africa (the Bichir, Polypterus) and America 
(the Bony Pikes, Lepidosteus). Lutken a restricted the 
scope of the Ganoids to the last-mentioned division 
(Muller’s Holostei), but ranged them as well as the 
Sturgeon-fishes (Muller’s Chondrostei ) in the category 
of distinct subdivisions among the Teleostean Physostoms. 
The free gill-arches alone, with the branchial la- 
mellae projecting beyond their free, outer (convex) mar- 
gin, are enough to distinguish the Sturgeon-fishes from 
the true cartilaginous fishes and approximate them to 
the Teleosts, with which they are also allied by several 
other points in their organization, e. g. the covering of 
the head with membrane-bones that distinctly represent 
the several component bones of the Teleosteous cranium, 
and the structure of the generative organs. Their in- 
clusion within the order of the Teleosts is indeed for- 
bidden not only by the above-mentioned characters 
( cliiasma and conus), but also b}^ the structure of the 
extremities, wherein the Sturgeon-fishes have preserved 
a great portion of the primordial cartilaginous radialia, 
as well as by the undivided chondrocraniuin and the very 
partially transformed notochord. But Lutken is, beyond 
doubt, fully justified in his opinion that the Sturgeon- 
fishes have far more in common with the Teleosts than 
with the true cartilaginous fishes. Doderlein * 6 too com- 
bined them together with the Teleosts and the true 
Ganoids into an order, Teleostomi, characterized by the 
completely ossified skeleton or at least by membrane- 
bones on the head and shoulder-girdle, by the free 
(joined to the cranium by articulations, sutures, or 
ligaments) hyomanclibular and palatoquadrate arches', 
and by the unarmoured pectoral fins' 7 . Among the 
Teleostoms they are distinguished by their fully hetero- 
cercal caudal fin, with the tip of the spinal column ex- 
tending quite or nearly to the end of the upper caudal 
lobe, and by their unilaterally rayed' paired fins. In 
Doderlein they rank, with these characters, as a sub- 
order ( Heterocerci ). In the Scandinavian fauna, which 
contains neither Lung-fishes ( Dipnoi ) nor Ganoids, it 
may suffice to have drawn attention to the relation of 
the Sturgeon-fishes to the Teleosts and the true carti- 
laginous fishes, which is adequately expressed by Mul- 
ler’s interpretation of them as a distinct order. 
Fam. ACIPENSERlDfiE. 
Body fusiform , with, five rows of large osseous bucklers. Four barbels in a transverse row on the under surface 
of the snout, in front of the protrusile mouth. No branchiostegal rays. 
In modern times the Chondrosteous order contains 
only two families, one of which, the American and 
Chinese Polyodontidce, with almost or quite naked body - 
and without barbels, is principally distinguished by its 
comparatively large mouth, open even laterally (on the 
sides of the head), and with upper jaw incapable of 
protrusion, the anterior extremity of the palatine arch 
being firmly united by ligaments to the under surface 
of the skull. Another important difference is that the 
Polyodontidce are without pseudobranchiae, those of the 
Sturgeons being exceedingly well developed, even func- 
tional as gills, with at least superiorly free branchial 
lamellae, on the inside of the opercula. 
On opening the pharyngeal and branchial cavities 
of a Sturgeon, the most striking difference from all 
the Teleosts meets us in the roof of the palate. This 
(fig. 284, mx — mpt) is a continuous, convex disk, with 
free margins both in front and behind, and capable, 
together with the toothless jaws and fleshy, tumid lips, 
of protraction forwards and downwards and of retrac- 
tion. On each side of the deep fold that hangs, covered 
with the thick mucous membrane of the pharynx, be- 
tween the free hind margin of the palatine roof and 
the under surface of the skull (parasphenoid bone) or 
posterior, fixed palatine roof with its continuation, the 
roof of the pharynx, we find an aperture. This hole 
a Om Ganoidernas Begroendsning og Inddeling, Vid. Meddel. Naturh. For. Kbhvn, 1868, sep. 
6 Steinmann and Doderlein, Elemenie der Paldontologie, pp. 540 and 556. 
c As opposed to the Lung-fishes. 
d As opposed to the primeval and extinct Placodermi (Pterichthys, Cephcilaspis, etc.). 
e Not lobate, or but slightly so, in contrast to the strongly lobate fins of the so-called Crossopterygii. 
