Midrasch zu Wajikra 11:30

1) (Vayikra 11:31): "These are what are tamei to you among all that creep": "what are tamei" (rather than just "tamei"): to include their skins (as well as their flesh). I might think (that this refers to) the skins of all of them. It is, therefore, written "These are (the skins of) what are tamei" — the skins of (Vayikra 11:30) the gecko, the land-crocodile, the lizard, and the sand-lizard. R. Yehudah says: The lizard is like the weasel (Vayikra 11:29). R. Yochanan b. Nuria says: Eight sheratzim have skins.