What Causes The Bumpy Ridges In Fingernails?

My fingernails have been changing over the past few months -- no trauma was experienced. My nails have developed ridges and a rougher surface (primarily on the thumbs). They have become a little thicker and are flattening out on the pointer, middle and ring fingers of both hands. They have become half and half pinkish brown and pinkish white, with the lunula (?) visible on only two fingers (one pointer and one thumb). And some fingers have a few splinter hemmorhages now and then (not that they grow out, they just eventually disappear). Any suggestions?