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Table S. Continued 18. Developing dorsal fin 1. with few (sS) or no melanophores. 2. with many (~) melanophores. 19. Pigment in dorsal fin 1. along fin rays with very few, if any, melanophores on membrane between rays. 2. abundant both along and between rays. 20. Pigment in anal fin 1. absent. 2. present but very light with only a few (s5) melanophores. 3. present but more prominent with many (~6) melanophores. 21. Pigment in pectoral fin 1. absent. 2. present but very light with only a few (s5) melanophores. 3. present but more prominent with many (~6) melanophores. 22. Pigment in caudal fin 1. along fin rays with very few, if any, melanophores on membrane between rays. 2. abundant both along and between rays. Presence and pattern of melanophores on the ventral to ventro-Iateral surfaces of the gill covers can also be diagnostic throughout the early development of these fishes. Such pigment is present on some larvae of all developmental intervals for all species except bluehead and flannelmouth sucker. It is rarely present on bluehead flexion mesolarvae and metalarvae or on flannelmouth flexion mesolarvae. Distinct oblique rows of three or more melanophores are often present along or near the ventral margin of the preopercle of white and mountain suckers (Figs. 31 and 74), .but are rarely present for most other speCIes. Another obvious diagnostic character for protolarvae and mesolarvae is the melano- phore pattern of the dorsal surface from behind the head to about two-thirds the distance to the last myomeres. Pigment here tends to be scattered with no distinct lines parallel to the dorsal midline for mesolarvae of most bluehead and mountain suckers (Figs. 44-45 and 72-73). Many flannelmouth and some white sucker mesolarvae have lines of melanophores lateral to the dorsal midline in which the melanophores tend to be in obli- quely oriented pairs or groups resulting in a distinctive "herring bone" or "tractor tread" pattern (Figs. 30 and 58). Extent of lateral body pigmentation is useful for mesolarvae through juveniles. Among flexion mesolarvae, for example, at least a couple melanophores are sometimes present between dorsolateral surface and the horizontal myoseptum of all but flannelmouth and razorback suckers. Even by the metalar- val phase, some razorback sucker are still without pigment in this region (Fig. 88). Among juveniles, only white sucker and some Utah sucker display large mid-lateral spots. White sucker have three spots (Fig. 35) while Utah sucker with lateral spots have only two distinct spots anterior to the vent (a faint or indistinct third lateral spot might be apparent in the caudal region of some Utah suckers). The scales of most white sucker and some Utah and mountain suckers greater than 30 mm SL are well outlined with pigment (Fig. 35). Distribution of pigment in various fms can be diagnostic for later larvae and juven- iles. Pigment along the rays of the dorsal and caudal fins is typical of all suckers considered herein. In addition, abundant melanophores on the membranes between dorsal and caudal fm rays are characteristic of all razorback juveniles (Fig. 91) and most razorback meta- larvae. In contrast, few melanophores are present on the membranes between caudal fin rays of bluehead and mountain sucker metalarvae and juveniles, dorsal fin rays of bluehead, mountain and Utah sucker meta- larvae, and dorsal fin rays of bluehead juveniles. Mouth characters are important in the diagnosis of adult catostomids. Unfortunately the mouths are insufficiently developed in all but the latest larvae and certain characters remain indistinct in the earliest juveniles (e.g., the lower lip lobes of some bluehead suckers up to 25 mm SL, Table 6). Mouth position remains terminal for some metalarvae and juveniles of mountain and razorback suckers up to 25 mm SL, but changes to low terminal or subterminal by 19 mm SL for all metalarvae of the other 31