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84 <br />forms were intermixed and that intermediates were present <br />(personal communications, 1975 and 1976). <br />Populations of bluehead suckers collected from the <br />Yampa and White Rivers in my study were polymorphic but <br />without the random intermixture seen in some of the above <br />studies. The highly-significant F statistic obtained by <br />analysis of variance of the CP/SL ratio at the four Yampa <br />stations indicates that means of ratios were somewhat <br />variable between stations and that variances within <br />stations were small enough to allow comparison of means. <br />No narrow-peduncled forms were found at Station Y-1, and <br />only two broad-peduncled individuals (CP/SL -'> 7 percent) <br />were found at Station Y-4 (Appendix 2 ). Internedi.ates <br />did occur, but among relatively-invariant populations at <br />Stations Y-2 and Y-3. Only at Station Y-3 did significant <br />numbers of intermediate and narrow-peduncled types occur <br />together. <br />Further statistical comparisons might expand upon the <br />p6rvasive occurrence of intermediate suckers at the Yampa <br />stations but could not dispute the almost complete absence <br />of mutually-occurring extreme forms at any station. This <br />suggests populations which have 1) been influenced by dis- <br />parate environmental conditions and reflected that influ- <br />ence morphologically, and 2) maintained some degree of <br />genetic integrity despite changes in physical environment <br />and community composition. The population at Station Y-4 <br />has experienced the most environmental influence <br />i <br />i