Crenate: scalloped, with rounded teeth.
Crenulate: with small scallops, evenly rounded and rather deeply curved.
Crepitation: a crackling sound or the production of such as by discharge of vapor or "bombarding": a cracking or creaking.
Crepuscular: active or flying at dusk.
Crescentiform: like a lunule or crescent.
Crescentric: lunulate.
Crest: a prominent, longitudinal carina on the upper surface of any part of the head or body.
Crested: see cristate.
Cretaceous: chalky white: the third, uppermost and latest of the three great divisions of the mesozoic or secondary rocks.
Cribrate: pierced with closely set, small holes.