1a.  Mouth terminal, front of upper lip at about the level of middle of eye; snout not extending beyond lips; snout length (A) less than eye diameter (B); pigmentation on forward lateral scales creating diamond-shaped pattern.
cypress minnow
Hybognathus hayi

1b.  Mouth inferior, front of upper lip below middle of eye; snout extends beyond lips; snout length (A) greater than eye diameter (B); pigmentation on forward lateral scales forming smooth-edged scale pattern, not diamond shaped pattern.
Mississippi silvery minnow
Hybognathus nuchalis