Four dimensional $3$-Lie coalgebras with two-dimensional derived algebras, and four-dimensional $3$-Lie bialgebras of type $(L_b, C_c)$ are classified.
It is proved that there exist three classes of four dimensional $3$-Lie coalgebras with two-dimensional derived algebra which are $(L, C_{c_i})$, $i=1, 2, 3$ (Lemma 3.1),
and ten classes of four dimensional $3$-Lie bialgebras of type $(L_b, C_c)$ (Theorem 3.2).