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

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;,ten OF 9 ski s AM r Sturgeons of the Genus Scaphirhynchus 187 difference between this species and Scaphirliynckus platorynchus; the �- former was said to have 20 or 21 ribs, the latter 10 or 11. \o ex- planation of the method of counting is given. The ribs are wholly chondrified and T rays taken by us fail to shoes- them. It is evident f"m dissection that the ribs are rather long anteriorly- but become :veld- shorter posteriorli, where they appear merely as trans- -. processes. It mai be questioned whether even the anterior elements should be termed ribs. In album the m, osepta appear to TABLE IN- CO]IPARISON OF THE SPECIES OF SCAPHIRII i-\CHCS T� CERTAIN- AIEASCRE.ME \" RATIOS A_ratios were derived arithmeticall}- from the original straight -line measurements. Stand- platorynchus album Ratio and ii length ;i �O No. (mm.) °f Range ]lean of Range Mean spec• spec I. Tout width: mouth to inner 100 -200 r 6 1.23- 1.36 1.28 1 .E: " ". I.74 200+ i 4 1.07- 1.42 1.23 12 1.6-- 2.00 1.80 to outer baroel: mouth 100 -200 6 1.32- L 65 1.54 1 3.40 _ - i -rbel 2001 47 1.27- 2.19 1.60 12 2 29 3.26 2,87 _- .ai,: mouth to inner bar- 100 -200 " 6 4.10- -4.5,5 4.29 1 bel 5.59 200-4- 47 4.00- 5.04 4.37 12 5.• ; -- 7.0n 6.31 4. Outer barbel length: inner barbel 100 -200 6 1.25- 1.4; .1.36 1 length 200+ 4i 1.17- 1.48 1.34 1.64 5. Snout tip to outer barbel:inner 100 -200 6 1.44- 1.92 1.i3 ]i 1 - -- ' 41 ;.yg barbel length 1• e 00+ I: 4' 1. 26- 2.50 1.64 12 2.63- 3.73 3.26 :inner barbel length 100 -200 j: 6 4.49 5.19 4.80 1 6.47 200+ 47 3.65- 5.76 4.47 12 6.35- 5 "00 ;•17 tenth lateral plate:in- 100 -200 6 1.90- 2.63 2.32 I tersuace between lateral and 200 t � 1.1 47 L_3 - , - .29' 2.37 13 0.55 L51 ].11 1 ventrolsteral series 8. Snout tip to outer barbel: height 100 -200 ! 6 2.73- 4.45 3.47 1 n o' tenth lateral plate 200 ,� _ 5. -3 length: height of tenth ]at- 100 -200 46 8.49 -12.00 9.60 12 1 4.12- 5.2f 14. go - eral plate 200+ 47 5.72- 9.33 7.69 9.12-11.30 �i ' 1. 10.02 ' Except for one specimen all values are below 3 69. be :�� anewhat better chondrified; thus the ribs are longer, especially posterior],-, than in platorynchus. This seems to be a minor differ- ence of degree, of far less importance than Forbes and Richardson's description suggests. Perhaps these authors counted cross sections of ribs revealed in longitudinal incisions of the body wall. If so, the lonLrer rih. of album would result in a higher count. Enlelixllnff's ol,servations on the ribs in :lcipenser seem to he similar to ours on .Scaphirhynchus.