  In his 1982 paper, Ogus defined a class of cycles in the de Rham cohomology
of smooth proper varieties over number fields. This notion is a crystalline
analogue of $\ell$-adic Tate cycles. In the case of abelian varieties, this
class includes all the Hodge cycles by the work of Deligne, Ogus, and Blasius.
Ogus predicted that such cycles coincide with Hodge cycles for abelian
varieties. In this paper, we confirm Ogus' prediction for some families of
abelian varieties. These families include abelian varieties that have both
prime dimension and nontrivial endomorphism ring. The proof is based on a
crystalline analogue of Faltings' isogeny theorem due to Bost and the known
cases of the Mumford--Tate conjecture.
