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

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PAPERS OF THE 'MICHIGAN ACADEMY OF SCIENCE, ARTS, AND LETTERS, VOL. XXXIX, 1954 (1953 MEETING) RIFER ST- RGEO.' \S OF THE UERICAN GENUS SCAPHIRHYNCHUS: CHARACTERS, DISTRI- BUTION, AND SYNONYMY REEVE --I. BAILEY Unirersiiy of 3fichigan FRANK B. CROSS Unirersity of Kansas, Lawrence, Kansas Nfishes, IO. G the many endemic genera of North :�merica.n freshwater one of the most distinctive and bizarre is Scaphirltynchus, which includes t«-t, p, , 'ies confined to the larger rivers of the in- terior lowlands, primarily in the _Mississippi basin. S. platorynehus (Rafinesque) is'the more common and widely distributed species and is the subject of considerable commercial exploitation. S. album (Forbes and Richardson) was not described until 1905 and remains one ui the least %cn of our larger freshwater fishes. Originally taken near the mouth of the Illinois River, it has since been reported definitely only from the mouth of the Missouri River and from the _Mississippi River at Keokuk, Iowa. The recent accumulation of new material of both forms enables us to verify their specific, though not generic, distinctness, present descriptive measurements and me- ristic counts, contrast the species in certain differential characters, list new records of specimens, and map the known geographic ranges. METHODS Except as noted below, the methods employed in taking measure - meits aiia couu --re those currently used by most American ich- tlivologists (e.g., Hubbs and Lagler, 1947: 8 -15). In the plate counts all clearly carinate scutes are included. In the series of dorsal plates the postoccipital is reckoned as the anteriormost (this is normally the first to bear a well- formed spine), but the predorsal plate is ex- cluded. In the lateral series the first plate counted is just behind the shoulder girdle (the tabular and posttemporal, which bear spines, . are excluded); at the posterior end small plates are counted if they 169 MTV x ��.,;