Talmud (Rodkinson Edition) — Book 1…
“ Have we not learned in a Boraitha, that one who caught one of the eight kinds of reptiles enumerated in the Scriptures, or who wounds them, is culpable and that this applies only to such reptiles as have skins, and only such a wound is called incurable which has been produced by the blood clotting in the skin and remaining there, even when no blood came to the surface? R. Johanan ben Nuri, however, states, that all the eight reptiles enumerated in the Scriptures have skins (and therefore one who wounds any of them is culpable; we see that they, disagree even as regards the Sabbath) . ”
