Here is a WDFW link with some better pictures: http://wdfw.wa.gov/fishing/shellfish/crab/identification.html.

Note that the term shore crab used in the regs really refers to two species in WA; both of the genus Hemigrapsus which is different than the North Atlantic/Baltic's shore crab (Carcinus maenasenus) shown in Drifter's link.

I happened to be in attendance when that rule change came before the Commission and it was pushed by Staff under the guise that Puget Sound beaches were being over harvested. Didn't ring true then and still does not plus additional info has come forth that the actual concern was regarding public beaches which comprise very little of the miles of P.S. beaches which owners strongly guard.
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Remember to immediately record your catch or you may become the catch!

It's the person who has done nothing who is sure nothing can be done. (Ewing)