ORDER VII. 
GANOIDEI. 
In the representatives of the Ganoid order the internal skeleton is either hony or else carti¬ 
laginous, and the scales which invest the surface of their body consist either of angular or 
rounded plates, of a hony base, and covered with an external layer of enamel, similar in structure 
to the enamel of teeth, else they assume the shape of bony shields; others still are perfectly 
naked. The caudal fin is more or less heterocercal, and the anterior margin of the fins often 
provided with a double series of shingle-like plates, or points the so called fulcrae. Several of 
them are provided with an accessory breathing organ placed under the opercle, and which is to 
he distinguished from a pseudo-branchia. Some of them are likewise possessed with spiracles. 
The swimming or air bladder is provided with an air duct, which communicates with the throat, 
as in many osseous fishes; but the rete mirabile is wanting. There are oviducts leading the 
eggs out, without allowing them to fall in the abdominal cavity. Oftentimes the intestinal 
canal exhibits a spiral valve, as in Plagios'omi. The manifold valves of the aorta, the free gills 
protected by an opercle, an accessory gill under the gill covers, and the abdominal position of 
the ventrals, are characters which the ganoids alone exhibit in combination. To these may he 
added a peculiarity in the direction of the optic nerves, which consist in not crossing one another 
before entering the orbit. 
Syn. — Ganoides, Agass. Rech. Poiss. foss. II, 1833, IX. 
Ganoidei, Bonap. Vert. Syst. 1837, 43 Catal. Pise. Europ. 1846, 4.— Agass. Nomencl. Zool. Pise., 1844. Mull. 
in Wiegm. Archiv fur Naturg. 1845, I, 129 &. 137. 
The structure and natural affinities of the fishes constituting the ganoid order have been made 
the subject of very special investigations by Prof. Joh. Muller, and which have somewhat modi¬ 
fied their classification as formerly proposed by Prof. Agassiz. Muller’s researches are the 
standard of all future investigations upon this strange and curious order of fishes, and which 
includes numerous extinct types, illustrated and described in the various works on Palaeontology 
or fossil remains. 
Family A MIA D A E } Baird. 
Opinions are at variance regarding the systematic position this family is to occupy in the class 
of fishes. Its representatives are but few, perhaps reduced to a single living species, which has 
been placed by some writers in the herring family, whilst others have associated it with some 
extinct types of past eras. Still others consider it as entitled to a place amongst Holostean 
ganoids, on the ground of the aorta being provided with five or six valves. 
Syn. — Jlmiadae, Bd Iconogr. Encyclop. II, 1850, 234. 
The genus Amia , so far unique in this family, is exclusively confined to the fresh waters of 
North America, and occurs chiefly in the southern and northwestern States, where they are 
known under the names of “mud-fish” and “marsh-fish,” and sometimes “dog-fish” also 
