Lice in Guinea Pig? How to tell if its a lice?

Hello. I just want to ask how will I able to tell if my cavy have lice? I noticed that in her white fur, there are black-brownish spots in her fur. I thought it was normal but they again when I tried to pull one of it and put it on a white sheet of paper, it looks like a lice to me, although I'm not sure.
   
Please help me.

http://www.guinealynx.com is a very helpful website for almost all things guinea pig! There is a complete section on guinea pig lice, mites, etc. and could probably help you determine what exactly you are looking at.