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

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Sturgeons of the Genus Scaphirhynchus 175 i, e`panside, with a sharp marginal carina and a median dorsal cluster of small retrorse spines near tip (these commonly obsolete in adults); no spiracle and no pseudobranchium; an accessory opercular gill that is poorly developed, consisting of only 20 to 25 short fila- ments; gillrakers short, fan - shaped, each provided with several soft rnin +: - Hill openings closely approximated, the branchiostegal me-ii- '..--d to isthmus near mid -line; upper caudal lobe ill WIL- an elongate filament that becomes relatively shorter with age; nostrils enlarged; eyes tint -; 4 fringed barbels; 4 heavily papillose lobes on upper lip and 4 fringed lobes on loner lip, of which 2 are Iocated at angles of mouth; clavicles not keeled; plates mostly share':-- - poinT '. of moderate to small size, numbering 14 to 19 in dorsal se-: lateral row, and 9 to 1.1 in ventrolateral file; 30 to 43 dorsal- I5 to 28 anal rays, 44 to 56 pectoral rays (the first a moder- ate} strong spine), and 28 to 34 pelvic rays; 6 (rarely i) pectoral radials; 8 pelvic radials; cartilaginous pleural ribs. THE SPECIES OF SCAPHIRHT_ \'CHUS :1 i4tudy of the original characterization of Parascaphirhyn- .., (Forbes and Richardson, 1905), especially scrutiny of the makes it apparent that the authors had a new species a< wt-li as Scaphirhynchus platorynchus before them. 'Nevertheless. a number of circumstances have led some contemporary ichthyu, to doubt, at least privately. the validity of S. album. Our specimens confi -m the bulk of the original characterization and provide proof c i is distinctness of S. album. Plate and Fin -Ray Counts Since the five lengthwise series of dermal plates are such a strik- ir::- , haracteristic of sturgeons, and since counts may be taker: with facility, all authors have dutifully recorded their numbers. These prove to be of high diagnostic value for certain species of .lcipenser and Ps^udoscaphirhynchus. In Scaphirltynchus, however, although there considerable individual variation in plate counts (Table I), differences between the species are so slight as to have no value in ifivntification and, probably, no significance. Fin -rah- counts, though difficult to make and disregarded by most students of the group, furnish excellent differential characters (Table I). For each fin, a1` lr!� a higher mean count than does platorynchus. In dorsal