Looks like snails to me. Those are shells on them, aren't they?

Interesting. Rather looks like they're embedded in the leaf. Is that so?

Or are they on the surface and easily brushed off?

I was able to brush them off with either my finger or a strong stream of water - some not as easily, but they didn't seem embedded.

This morning I was able to look a little closer - when I brushed one off a leaf, it did have legs and was crawling around.

Any other ideas out there on what this can be?

Milk slugs, different species group from the big slimers, not easily caught in beer traps. Place damp newpapers beneath the plants and gather them up after the sun comes up. Lots will be stuck to the bottom. Go out at night and drench plants with strong (cold) caffeinated coffee. It's a neurotoxin, messes up feeding. Pull back any mulch and wait until the problem peaks to start mulching, usually when cool and damp weather gives way to warm and dry. Good luck, it's a seasonal problem.

Those look to me like aphid "mummies". It's a good thing - I always leave those where they are. They can be caused by a fungal infection or a parasitic wasp:

**Among the most important natural enemies are various species of parasitic wasps that lay their eggs inside aphids. The skin of the parasitized aphid turns crusty and light brown, a form called a mummy. The generation time of most parasites is quite short when the weather is warm; when you begin to see mummies on your plants, the aphid population is likely to be reduced substantially within a week or two.**

Here is a link that might be useful: Aphids - scroll down to 'Natural Enemies'

Here's a link to some pictures of cotton aphids for comparison...

Here is a link that might be useful: NCSU gallery

Are these scale insects?

Here is a link that might be useful: {{gwi:43537}}

I'm with Carolb (unless they're still alive)

They look a lot like the crispy, dead cabbage aphids that remained on the back of my leaves
after I sprayed them with a neem oil solution

See the link below to see what they looked like before I sprayed

Here is a link that might be useful: Cabbage Aphids

I'm with Carolb too.

What she is saying is they are mummies, not just dead aphids. Mummies are dead aphids killed by parasitic wasps which have laid their eggs in the bodies of the aphids. Those eggs will become more parasitic wasps which, if they multiply in sufficient numbers will decimate the aphid population in that garden.

Mexican bean beetles have their own parasitic wasp which works the same way.

Jim