BIOT.—­A brilliant little ring-plain, scarcely more than 7 miles in diameter, standing in an isolated position in the Mare Foecunditatis N.E. of Wrottesley.  There is a number of bright streaks in its neighbourhood; and a few miles E. of it, in the hilly region W. of Santbech, another conspicuous crater of about the same size.

BORDA.—­A ring-plain about 25 miles in diameter, S.S.W. of Santbech, with a rampart low on the N. and S., but elsewhere of considerable height, and a very conspicuous central mountain.  A wide deep valley flanked by lofty mountains extends from the N. wall for many miles towards the N.W.  It is an especially noteworthy object when the W. wall of Santbech is on the evening terminator, as its somewhat winding course, indicated by the bright summit-ridges of the bordering mountains, can be followed some hours before either the interior of the valley or the region between it and Santbech are in sunlight.  Among the mountains W. of Borda there is a peak more than 11,000 feet in height.

SNELLIUS.—­A very fine ring-plain, 50 miles in diameter, S.E. of Petavius, with terraced walls, considerably broken on the S.E. by craters, &c.  It rises on the E. nearly 7000 feet above a dark floor, which contains a central mountain.  N.E. of Snellius is a smaller ring-plain (Snellius a), and due E. a curious rough plateau, bordered on the N. and S. by a number of small craters.

STEVINUS.—­A somewhat larger ring-plain, S. of Snellius, with a border rising on the S. to more than 11,000 feet above a dark interior, which includes a bright central mountain.

REICHENBACH.—­A very abnormally-shaped ring-plain, about 30 miles in diameter, with a rampart nearly 12,000 feet high.  The border is broken on the W., S., and E. by craters and depressions, and on the N. is flanked by two overlapping ring-plains, a and b.  On the S.W. lies a magnificent serpentine valley, fully 100 miles in length and about 12 miles in breadth at the N. end, but gradually diminishing as it runs southwards, till it reaches a depression N. of Rheita, where it terminates:  here is scarcely more than 4 miles wide.

RHEITA.—­A formation, about 35 miles in diameter, S. of Reichenbach, with regular lofty walls, rising at a peak on the N.E. to a height of more than 14,000 feet above the interior, on which there is a small but prominent central mountain, a smaller elevation W. of the centre, and two adjoining craters at the foot of the S. wall.  On the E. originates another fine valley, very similar to that already mentioned in connection with Reichenbach.  It runs in a S.S.W. direction, is about 100 miles in length, and, in its widest part, is about 12 miles across.  Like the Reichenbach valley, it terminates at a small crater-like object, which has a border broken down on the side facing the valley, and a small central hill.  About midway between its extremities, this great gorge is crossed by a wall of rock, like a narrow bridge.