The snail is a Variegated Amphissa (Amphissa versicolor). [Unfortunately, this isn't a great example of this species because these individuals are covered by a bryozoan so their true shells are hidden.]
Here's a close-up of the egg capsules on the right side:
From this angle you can see that the capsules are two-parted. There's a rounded basal portion attached to the kelp, and an upright vertical section that looks like a very tall cap. These capsules are sometimes described as helmut-shaped, but they often remind me of Hershey's Kisses!
The developing embryos are in the rounded basal portion. You can see them when viewed from above (next image):
Eventually the embryos will hatch out as swimming larvae and will develop in the plankton for a while before returning to shore and undergoing metamorphosis into crawling juvenile snails.