What is Chomet?
Rashi: It is Limtza (in old French, i.e. Chilazon, i.e. a snail).
QUESTIONS ON RASHI
Rashi writes that Chomet is Limtza (in old French, i.e. Chilazon, i.e. a snail). In Chulin (126b), Rashi says that a Chomet lays eggs. Snails do not lay eggs!
Sifsei Chachamim (Megilah 6a): The Aruch holds that there are several kinds of Chilazon - like a fish, worm, Chomet or snail. He says that all of them have shells. 1
Perhaps Rashi refers to a kind of Chilazon that lays eggs. Alternatively, here Rashi explains like R. Gershom (Bechoros 38b), and elsewhere he did not. (PF)