CASATUS.—­A large walled-plain, about 50 miles in diameter, S.E. of Blancanus, near the limb, remarkable for having one of the loftiest ramparts of all known lunar objects; it rises at one peak on the S.W. to the great height of 22,285 feet above the floor, while there are other peaks nearly as high on the N. and S. The wall is broken on the E. by a fine crater.  There is also a crater on the N.W. side of the very depressed floor, together with some craterlets.

KLAPROTH.—­Casatus partially overlaps this still larger but less massive formation on its S.E. flank.  The walls of Klaproth are much lower and very irregular and broken, especially on the W. There are some ridges on the floor.  The neighbouring region is covered with unnamed objects, large and small.

EAST LONGITUDE 40 deg.  TO 60 deg.

FLAMSTEED.—­A bright ring-plain, 9 miles in diameter, in a barren region in the Oceanus Procellarum, N.E. of Wichmann.  It has a regular border (broken at one place on the N. by a gap, which probably represents a crater), rising to a height of about 1400 feet above the surrounding plain.  A great enclosure, 60 miles in diameter, lies on the N. of Flamsteed.  It is defined by low ridges which exhibit many breaks, though under a high light the ring is apparently continuous.  Within are several small craters and two considerable hills, nearly central.

HERMANN.—­A ring-plain, about 10 miles in diameter, in the Oceanus Procellarum, W. of Lohrmann.  It is associated with a group of long ridges, running in a meridional direction and roughly parallel to the coast-line.

LETRONNE.—­A magnificent bay or inflexion in the coast-line of the Oceanus Procellarum, N.N.E. of Gassendi, presenting an opening towards the N. of nearly 50 miles, and bounded on the S. and S.W. by the lofty Gassendi highlands.  Its border on the W., about 3000 feet high, is crowned with innumerable small depressions.  The interior includes four bright little mountains, nearly central (three of them forming a triangle), a bright crater on the W. side, and several minor elevations and ridges.  On the plain N. of the bay, is a large bright crater, from which a fine curved ridge runs to the central mountains.  If Letronne is observed under oblique illumination, the low mounds and ridges on the Mare outside impress one with the idea that they represent the remains of a once complete N. wall.

BILLY.—­A ring-plain, 31 miles in diameter, S.E. of Letronne, with a very dark floor, depressed about 1000 feet below the grey surface on the W., and a regular border, rising more than 3000 feet above it.  There is a narrow gap on the S., and indications of a crater on the N.W. rim.  Two small craters stand on the S. half of the interior.  The formation is flanked on the S.W. by highlands.