jmc

We name those two perfect squares on the blackboard $a^2$ and $b^2$. We are given that $a^2-b^2=99$. Factoring, we get $(a-b)(a+b)=99$. Since the two perfect squares have two other perfect squares between them, we know that $a-b=3$. Therefore, $a+b=33$. Adding the two equations together, we get $2a=36$. Therefore, $a=18$ and $b=15$. Thus, the sum of the two perfect squares is $a^2+b^2=324+225=\boxed{549}$.