Commentary for Shabbat 270:2

Two Foreskins - two foreskins, one on top of the other. Some say [it means] two penises.

The Rosh begins by quoting the Talmudic sugya on 135b, and then says: The argument of Rav Huna and Rav Hiya bar Rav revolves on this point. The one who says that we don't override Shabbat to do a Brit for a baby born through Caesarean or double-foreskin is agreeing with Rabbi Assi. But this is a minority opinion. Since we projected this debate onto the Beraita('ketanai'), and the rabbis seem to disagree with Rabbi Hama, and say that a child born to a slave-woman who hasn't immersed and is therefore not impure nonetheless has his Brit on the eighth day - this indicates that the Rabbis didn't hold like Rabbi Assi. And these Amoraim who argue simply never heard of the Beraita, because if they had heard of it, they wouldn't have simply said their statements, but would have quoted their source. Since they hadn't heard of it, perhaps if they had known it they would have simply followed the Rabbis on this point, because the halacha always follows the majority. However, the "Halachot Gedolot" is unsure about how to rule on this point. And therefore, because there is doubt, then we rule as follows: we do a circumcision on the eighth day, but not if it falls on Shabbat.