I listed them together with my lab experience. For example, I said: Research associate, Undergraduate Researcher in X lab for X years; X publications. I then described the topic of my research but never actually said what the titles of the publications were (all pubs were on related topics). You can list the titles/citations in your secondary essay (or attach a CV to the secondary--that's what I did). I'm not sure if they like you to attach CV's, but I did it anyway.