River Sturgeons of the American Genus Scaphirhynchus: Characters, Distribution, and Synonymy

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Sturgeons of the Genus Scaphirhynchtts 185 di,+,ributed over the body- than those in album, in which these strue- t; r, s are mostly mere spicules. The difference is of degree rather than of kind. Most of the belly is naked at all ages in album. though large specimens may have small scattered specimens scutes lterally. near the pelvic fins, or on the breast. In young also, the bell' is naked, but adults have an irregular mosaic of rather large, rhomboidal scutes covering the ventral surface. The presence 'r =mantes is usually apparent in fish longer than 200 mm.; but a �n naked strip may persist in fish up to and beyond 300 mnl• r In the interspaces above and below the z cleusl series In albzun ;the the ossifications are typically larger in p J strip between the lateral plates and the midventral plating usuall 1 � - I9. � ♦- cz- —. • • % �• m o :1 • •~ Q y I ♦ J STCNDI.-D LENGTH (MW I ic. 7. Scatter diagram showing size Variation in the proportional length of the air bladder and difference between the species of J'cap;iiriignchjs extends back about as far as the origin of the anal fin; in platorynchus ±ii, strip terminates a short distance before or behind the origin of ti., dorsal fin (in both species the interspace contains m any small ossifications). Air bladder. —The air bladder is thick - walled anct is connected to the pharynx by a large pneumatic duct. Forbe_ and Richardson (190 : �l) stated that the length of the air bladder i� contained 5 times in the length of the head and body in platorgnchus, 5 times in +_ ,+ r,f albztm. �s shown in Tables II and III and in Figure , his i:- an oversimplification. although the air biadiie: ir. p- 1 is notably larger than in album, this character shows marked onto - genetic change: the length of the air chamber in platnr��nchus increases from 8 or 9 per cent of the body length in fish of 150 mra. to approxi-