Placoid scales are represented by oral scales and dermal scales.
Oral scales (Fig. 2D–M) are up to about 1.5 mm in height and are
characterized by an anteriorly inclined, thin, oval crown that rests
on a basally pointing diamond-shaped root. Their slanting crown
surface is flat or gently convex and smooth except at the base where
a distinct knob tends to extend basally (Fig. 2I). Dermal scales
(Fig. 2N–R) are up to 1 mm in height and are characterized by
a massive crown and bulbous root. The crown is circular or oval in
apical view and is flat or gently rounded, but its apical surface is not
slanted and a knob-like extension does not occur as in the oral
scales. The roots of both oral and dermal scales generally show
a few scattered, small pores.