Cyrillus is a lunar impact crater located on the northwest edge of Mare Nectaris.

The walls of the broken formation of Cyrillus remain intact until the point of junction with Theophilus.

[3] A tiny crater with bright rays on the east side of Cyrillus has been named Shioli.

[4] A point to the east of Shioli is the proposed landing site of Japan's SLIM lander.

[5][6][7] By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Cyrillus.