49 2 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 ab 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. Eostrum 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 fulcra. 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 



