  It is well known that the subvariety lattice of the variety of relation
algebras has exactly three atoms. The (join-irreducible) covers of two of these
atoms are known, but a complete classification of the (join-irreducible) covers
of the remaining atom has not yet been found. These statements are also true of
a related subvariety lattice, namely the subvariety lattice of the variety of
semiassociative relation algebras. The present article shows that this atom has
continuum many covers in this subvariety lattice (and in some related
subvariety lattices) using a previously established term equivalence between a
variety of tense algebras and a variety of semiassociative r-algebras.
