The white half-moon at the base of the nail is called the Lunula and is the leading edge of the Matrix where the nail plate cells are 'born'. The longer the lunula, the thicker the nail plate. One can usualy see the Lunula on the thumbs, forefingers, middle fingers and a little bit on the ring finger, but rarely on the pinkie finger. If you do not see the Lunula on your nails, it just means that your nail plate is thinner because of reduced nail plate cell production. This is always genetic and doesn't mean that there is anything wrong with your nails.