At a New Jersey beach yesterday I noticed that the incoming tide was bringing jellyfish up to shore. I was in water up to my chest and discovered that although I like to look at jellies at the aquarium, being in the water with them made me a tad squeemish.
I assumed that these were the common moon jellyfish, but based on a little online research I'm now convinced that they were many-ribbed hydromedusae. A lot of them were washing up on the sand, where they looked very much like pieces of ice from some beachgoer's cooler. I touched one of them gently with my finger and found it surprisingly firm (harder than JELL-O). A moon jelly might have stung me, as it certainly would have stung the little girl nearby who had gathered about ten of the creatures from the beach and arranged them in a line.
For a good approximation of what I saw, I direct you to Herb Segar's stock photography website, where he has good pictures for sale of many-ribbed hydromedusae both on the New Jersey sand and in the water.