I believe the only member of Amaeidae from that area which reaches anywhere
near the size of your largest specimen is Collisella dalliana.  That species
however is not heavily ribbed, so I would guess your specimens (if you are
sure they are all the same species) are Ancistromesus (Patella) mexicana.
Another characteristic to look for is that Ancistromesus tapers anteriorly,
so the front end of the shell looks bluntly "pointed", while the Acmaea
limpets are broadly rounded at the front end.
Paul Monfils
Rhode Island