Members of this genus are primarily lake dwellers, but two cold water species, C. nigritus and C. coloradensis, are especially important in the west. Nymphs are small to medium in size, have three tails equal in length, and rather large heart-shaped gills, which are double on segments 1-6, or 1-7. The outstanding feature of the adults is the freckled appearance of their bodies. Wings of the female have brown markings on the leading edge and both sexes have two tails.
