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Once melanophore pigmentation is sufficiently established, one of the more useful surface pigment characters is the extent of pigmentation on the ventral midline between the heart region and the vent (Table 5). Longnose, white, and mountain suckers typically have a continuous line of mid ventral pigment with over 20 melanophores (Figs. 30-32, 34,72-73, 98-101,103), at least through the larval period. Extension of this pigment line into the branchial region anterior to the heart is common in longnose and white suckers but rare in mountain sucker. Among the others, only bluehead sucker occasional have as many melanophores along the ventral midline, but the line is either shorter or distinctly discontinuous (Figs. 44-45). Complete absence of melanophores along the ventral midline is rare among Utah, bluehead, and flannelmouth larvae but common for razorback sucker larvae. Unlike the other species, razorback sucker larvae have not been observed to have more than 6 melanophores along the ventral midline (Figs. 85-89). Presence and pattern ofmelanophores 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 meso larvae. This pigmentation is sometimes present as a distinctive oblique row of three or more melanophores along or near the ventral margin of one or both preopercles in longnose, white, and mountain suckers (Figs. 31 and 74). Another obvious diagnostic character for proto larvae and meso larvae is the melanophore pattern on the dorsal surface from behind the head to about two-thirds of the distance to the last myomeres. Pigment here is scattered with no distinct lines parallel to the dorsal midline in most mesolarvae of blue head and mountain suckers (Figs. 44-45 and 72-73). Many flannelmouth sucker and some white sucker meso larvae have lines of melanophores lateral to the dorsal midline in which the melanophores tend to be in obliquely oriented pairs or groups resulting in a distinctive "herring-bone" pattern (Figs. 30 and 58). Extent of lateral body pigmentation is useful for meso larvae through juveniles. Among flexion meso larvae, for example, at least a couple melanophores are sometimes present between dorsolateral surface and the horizontal myoseptum of all but mountain and razorback suckers. Even by the metalarval phase, rare specimens of longnose and razorback suckers are still without pigment in this region (Fig. 88). Among juveniles, only white sucker often have three large, distinct, mid-lateral spots on the body: one anteriorly between the head and dorsal fm; one under the dorsal fm; and one near the end of the caudal peduncle (Fig. 35). Longnose sucker occasionally have a similarly large and distinct caudal-peduncle spot and Utah sucker rarely two comparable spots anterior to the vent (possibly with a faint or indistinct caudal spot). The large, distinct, caudal-peduncle spots observed on many white and some longnose suckers should not be confused with the small but sometimes prominent concentration of pigment sometimes present in the same location on these and most other species. The scales of most white and longnose suckers and some Utah and mountain suckers greater than 30 mm SL are well outlined with pigment (Fig. 35). Distribution of pigment in various fins can be diagnostic for later larvae and juveniles. Pigment along the rays of the dorsal and caudal fins is typical of all suckers considered herein. In addition, notable pigmentation (more than just a few melanophores, sparsely scattered to abundant) on the membranes between principal dorsal-fin and caudal-fin rays is characteristic of most metalarval and nearly all juvenile razorback suckers (Fig. 91). In contrast, the membranes 29