I have something further to add with reference to [=with respect to, in regard to] what was said earlier.关于我先前说过的话，我想再补充一些。

I am writing in reference to your recent letter.我这封信是对您最近来信的回复。

The course covers ancient history with special reference to the Roman Empire. [=the course is about ancient history and especially about the Roman Empire]这门课程讲述古代史，特别是罗马帝国史。