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There was also a strange decline in the numbe_ cf snail species noted • in the study area. In October, 4 species xere found, xhich declined to 2 species in March and one in July. No reason was apparent for this de- cline. Although water levels xere generally lox, xater quality (for those pa_Yameters measured) did not appeaz to be limiting. The only group to shox a marked increase in number of species from October to July xere the beetles (Ccleoptera) xhich rent from 2 to E species. Changes in the occurence of five major insect orders are shoxn in Table 5-9• In Table 5-10 the dominant species or genus of four insect groups from the North Fork October collection are comoazed xith collections from three other azeas~ the upper Gunnison drainage as a xhole (Wiltzius, 1967), a previous collection from the~loxer North Fork (Colorado Division of 'r,'i1d11fe, unpub.) and a 1972 collection from the Crystal River, xhich 11es just northeast of the North Fork drainage over McClures Pass. (Thorne, 1973)• The following summarizes the comparison. hla5~`'lies -- r,rheme=ella spp. xas the numerical doninant in all but the Gunnison drainage as a ~7hole, where Eaetis sp. xas dominant, and in the July sample of the present study xhen Tricorti~thodes xas dominant. Out of a to'a 1 of 17 may~'ly taxa, six xere found in the ?aonia study area. Caddisflies -- Members of 4ydropsvche xere numerical dominants in all studies, except the July sample of the present study xhen i,eucotrichia xas do,~:irant. Nine o_° the 17 caddisfly taxa xere found in the study area. St,oneflies -- Dominant taxa all differed in the four studies. Six of the 12 stonefly- taxa xere found in the study area. True flies (nor.-chironomid) -- In the present studies the chironomids • were numerical dominants at a'_1 times of the yeaz, hoxever Athrix or Simullum species xere most common in other studies. This difference is probably due 5-5