Laserfiche WebLink
Sturgeons of the Genus Scaphirhynchus 183 <br />of the barbels provides one of the quickest and most reliable means <br />identification of these species: the inner barbel is contained in <br />outer 1.17 to 1.48 times in platorynchus, 1.64 to 2.41 times in <br />album (Table IV). <br />The structure of the barbels, as well as their positions and lengths, <br />is distinctive of the species. In platorynchus the inner barbel is rela- <br />tively heavy-, with a basal diameter about three fourths that of the <br />longer barbel; in album the short inner barbel is slender, with a basal <br />+er about one half as great as that of the outer barbel. Prob- <br />,;ore important are differences in the fringing, that in album <br />being everywhere less well developed than that in platorynchus. In <br />platorynchus there are three rows of prominent papillae subequal in <br />size, one series on the ventral (anterior) edge and one projecting from <br />each side of the dorsal (posterior) surface of each barbel. In <br />J <br />p -6 <br />C � <br />Q <br />Ps_ <br />w <br />Z <br />♦ ♦ <br />• <br />♦ ♦ • 5 as�:n*dws <br />• ♦S xoua <br />i <br />ro STANDARD LENGTH (MM) <br />I•IG. 5. Sicatter diagram showing proportional length of inner barbel in <br />the species of Scaphirhynch wa <br />the two dorsal series of papillae are uniformly better de .;::,,, i than <br />the ventral file, which is imperfectl- developed or, frequenth , en- <br />tirely lacking. Also, the fringing on the longer barbel is usuall- <br />stronger than that on the shorter one, in which even the dorsal orna- <br />Iiwn ation may be reduced to a few tiny- projections. In the illustra- <br />tion by Forbes and Richardson (1903: facing p. 44), the barbels of <br />platorynchus are rather well shown, but the papillae on the barbels of <br />mount are better developed in their figure than in our spec•imuns. <br />Dorsal- and anal fin bases. —The relative basal lengths of the <br />median fins seem not to change with age. In each of these fins the <br />rapt• length is shorter in platorynchus than in album (Tables II <br />ai: ' Ili but there is some overlap in both measurements. For <br />example, the anal -fin base varies from 3.9 to 5.1 per cent of the stand- <br />ard length in 16 examples of platorynchus (4.6 per cent or less in 88 <br />