This is a scallop (I've been doing some more macro photography of shells this week).
At least, it is in English. In Dutch (and in French and in German and probably in other languages too) we have a more poetic name for it: Sint-Jacobsschelp (Saint James' shell). There's plenty of lines in it, but as a whole it is a symbol used by pilgrims walking from wherever to Santiago de Compostela (Heidi Egerman published a series of blogs on walking this "camino"), where Saint James is burried ("Santiago" means Saint James). These pilgrims follow certain lines through Europe and everywhere along those lines you'll find this very same symbol.