  We describe first-degree prime ideals of biquadratic extensions in terms of
first-degree prime ideals of two underlying quadratic fields. The
identification of the prime divisors is given by numerical conditions involving
their ideal norms. Interestingly, the correspondence between these ideals in
the larger ring and those in the smaller ones extends to the divisibility of
principal ideals in their respective rings, with some exceptions that we
explicitly provide. Finally, we hint at possible applications of this
correspondence.
