Smith, G. R. (Museum of Zoology, Univ. of Michigan, Ann Arbor 48104) and R. K. Koehn (Dept. of Ecology and Evolution, State Univ. of New York, Stony Brook 11790) 1971. Phenetic and cladistic studies of biochemical and morphological characteristics of Catostomus. Syst. Zool., 20:282–297.—Sixteen of the nominal species in the genus Catostomus, predominantly in western North America, form a progressive morphological sequence in which adjacent forms are similar and perhaps not reproductively isolated. Several cladistic estimates indicate divergence in two primary lines or directions. The oldest cladistic furcation is phenetically trivial. Significant phenetic trends indicate evolution at several levels. The dominant trend involves osteological, oral, and hemoglobin characteristics leading to the mountain suckers. Secondary phenetic trends in body shape and in size of fins and scales have led to adaptations for life in large rivers in three separate lines. Two phenetic trends, involving meristic and serum protein characters, are involved in the adaptation of populations to local climatic conditions.