(IAU Directions) RICCIUS.--A ring-plain, 51 miles in diameter, of a very irregular type, S.W. of Stiborius. It is enclosed by a complex wall (which is in places double), broken by large rings on the S. The very conspicuous little ring-plain Riccius A is situated on the N. of it, and other less prominent features. The interior includes a bright crater and some smaller objects of the same class.
- Depth data from Kurt Fisher database
- Westfall, 2000: 1.72 km
- Cherrington, 1969: 1.79 km
- Satellite craters Riccius B, E and M are on the ALPO list of banded craters
- The name Riccius was by introduced by Riccioli. According to Whitaker (p. 214), it designated the present crater.
- The IAU currently regards the name as honoring two men:
- Augustine Ricci (fl. 1513), an Italian astronomer also known (according to astronomical historian Robert Garfinkle) as Augustinus Riccius, Agostino, Ricius and Augistini Ritii. He is best known for the book De motu octavae spherae ("On the Motions of the Eighth Sphere"), apparently first published in 1513 and reprinted in 1521. Augustine Ricci seems to be unknown in Who's Who on the Moon by the twin brothers Cocks (1995).
- Matteo Ricci (1552-1610), an Italian mathematician and geographer, and early missionary to China.
- Matteo Ricci is the identification of "Riccius" made in the BAA's unofficial Who's Who in the Moon. The name Augustinus Riccius was noticed by Garfinkle in the biographical encyclopedia on page XXXI of Riccioli's book, and added to the IAU database, through his efforts, as a second honoree in 2005 (Matthaus Riccius is listed on page XL).