Striae that are composed of two rows of areolae are termed biseriate.
Much of the diatom literature uses "doubly punctate" to describe striae composed of two rows of areolae.
Image Credit: Marina Potapova
Biseriate striae are composed of two rows of areolae. Here the biseriate striae of Rossithidium nodosum are shown in a SEM image. Note that in some species, the biseriate striae are quite visible in LM. In other species, they may not be discernable without SEM.
Image Credit: Pat Kociolek
Biseriate striae are a distinguishing character of the genus Gomphoneis. Here, the biseriate striae of G. loweii are prominent in an LM image.