Melanochlamys diomedea eggs
These eggs belong to a sea slug - I don't recall spotting any of the adults, but they must be pretty abundant considering the number of egg cases that I saw on the beach. They may have been buried in the sand - had I dug near the eggs I may have found one.
Similar species: Headshield Slugs
Uploaded Feb 25, 2015. Captured Feb 24, 2015 14:36 in 25643 Marine View Drive, Des Moines, WA 98198, USA.