Pacific Plate Limpet, Tectura scutum, or Lottia scutum
Had quite a bit of difficulty determining the scientific name of this limpet. The preferred name in our area, the Salish Sea, is Tectura scutum although the majority of the references I read named the species, Lottia scutum. This specimen was found on the underside of a small rock. This photo is a full frame at 1:1, this little limpet is only about 8mm in its longest measurement. So, when on the beach picking up a small rock can provide all sorts of interesting photographic subjects.
''Lottia scutum'' is a species of sea snail, a true limpet, a marine gastropod mollusk in the family Lottiidae, one of the families of true limpets.