492 : FISHES CHAP. 
the eyes, its value as a tactile organ must not be overlooked. 
Polyodon may attain a length of 5 to 6 feet. The time of 
spawning varies, according to locality, from March to June. 
Nothing is known of the development of Polyodon. Young less 
than 6 to 8 inehes in length are unknown, and specimens of this 
size are very rarely seen. The jaws are furnished with minute teeth 
until the Fish is about half-grown, when they become edentalous. 
Caviare is made from the eggs, and the centres at. which this 
industry is carried on are chiefly situated along the course of the 
Mississippi. The second species, Psephurus gladius, inhabits the 
Yang-tse-Kiang and Hoangho rivers of China, and differs from 
Polyodon in the conical shape of its rostrum and the smaller 
number and larger size of its fulcra. Psephurus is stated to 
reach a length of 20 feet. The family is represented in the 
Eocene of Wyoming by the genus Crossopholis, which is note- 
worthy for the retention of trunk scales in the form of small, 
somewhat quadrate denticulated discs, arranged in oblique rows. 
Fam. 7. Acipenseridae.—In the Sturgeon family the body 
is elongate, cylindrical, and somewhat bulky. Rostrum well 
developed and often massive, with a transverse row of simple or 
branched preoral barbels on its ventral surface. Mouth small and 
remarkably protrusible. Jaws devoid of teeth except in the larvae. 
As in the preceding family, the primitive rhombic squamation 
is confined to the upper lobe of the tail, which, like the dorsal 
and anal fins, is furnished with fulera. Elsewhere the scales are 
represented by five longitudinal rows of large bony scutes and 
by intervening small scattered ossifications. The anterior dermal 
ray of the pectoral fin is stout and spine-like. The dermal 
bones of the cranial roof suturally articulate with one another 
to form a continuous shield, uninterrupted by lateral vacuities. 
A median dermal bone in the occipital region transmits the 
occipital sensory canal. The opercular series is represented only 
by an opercular bone. 
The family includes but two genera, Acipenser (Fig. 290) and 
Scaphirhynchus, and about twenty species, confined to the seas, 
estuaries, and rivers of the temperate and north temperate regions 
of the northern hemisphere. -Acipenser includes the more typical 
Sturgeons, and is distinguished by the presence of spiracles, and 
by the fact that the longitudinal rows of scutes remain distinct 
to the base of the caudal fin. There are probably about fifteen 
