This topic was split from a discussion on the Los Angeles board. If you have tips on where to find Cantonese snails with black bean sauce in the L.A. area, please see this thread:
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The snails/escargots described here are called periwinkles. They are kind of on the chewy side, and they are definitely NOT American chinese food, as I remembered eating those back in Hong Kong.
Conch is a heck of a lot bigger, although I can see where they are similar in the chewiness factor. I never care for periwinkles, especially when I have to bite down to make sure I get the meat part and not the entrails.