help with identification

[thalassa]

Hello!

I'm impressed with how easy it seems for you guys to come up with an identification. Some of the shells I find, I finally found a name for (or at least I think I did  ;D) but more often I remain clueless.

Has anybody any idea what these might be?

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The first  one is broken and very eroded, but still I would like to know what it is . It's 100 mm long. (aegean sea)
The second one is 60 mm long and comes from Chrissi island (libyan sea) but it doesn't look like any of the shells I've seen there. During summer though, they sell shells on the island for the tourists. Could it be that it comes from somewhere else?

Any help would be greatly appreciated!