We picked one up, and this is what it looked like on the tip of Eric's finger:
And here's another spread out on my mother's hand:
The view above made us laugh and led us to make up a name for this gelatinous animal — the "Sombrero Jelly."
Note the tiny black dots around the perimeter...the peak in the center with a gray smudge on top...and four radiating beige lines on the flat portion (like spokes on a wheel). (If the medusa is a clock, the beige lines are at about 2, 4, 8, and 10 o'clock.)
We weren't certain which way was up. Was the animal right side up, or upside down? We needed to submerge it in water so it would orient itself.
You'll laugh at me and the next picture, but it's a good lesson in transparent camouflage. First I tried to place the medusa in a shallow pool of salt water on the beach:
Can you see it? It's there, believe me. Right in the center of the picture. If you look very closely for a circular outline and the four radiating spokes, you might be able to find it. But don't worry if you can't. As mentioned, it illustrates just how effective it is to be transparent!
Then I remembered that I had a very small plastic container in my backpack. So I filled it with salt water and placed one of the medusa in the water:
Now you can see the animal in its natural position. They had been washing ashore and we had been holding them upside down!
It has a shallow domed bell at the top. The black dots around the perimeter mark the positions of hundreds of short tentacles. The protuberance hanging down in the center is called a peduncle and there are four frilly lips at the tip of it. The four beige radiating lines are gonads.
Not a great picture, but below is one more view looking up into the mouth/lips with the four radiating gonads and the rim of tentacles in the background.
I'm not 100% certain, but my best guess for this species right now is a hydromedusa called Eutonina indicans, sometimes called an Umbrella Jelly. I'll be checking in with a hydromedusa expert to see if she can confirm the identification.
Has anyone else been seeing sombreros or umbrellas washing up on local beaches? :)
ADDENDUM (6 December 2013): Yes! Claudia Mills (University of Washington) has confirmed this as an Umbrella Jelly (Eutonina indicans). Thanks, Claudia!