The upper (suprarostral) and lower (infrarostral) supportive jaw cartilages have pigmented and keratinized jaw sheaths. The relative amount of dark keratinization (width in longitudinal dimension) of a sheath sometimes is useful for distinguishing among tadpoles.
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Narrow Sheaths-dark for less than half the width
Medium Sheaths-dark for about half the width
Wide Sheaths-dark for nearly the entire width
Other jaw sheath characteristics are sometimes useful to distinguish among species.
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