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. HANSTEEN.--A somewhat larger ring-plain, with a lower and more irregular rampart, rising on the W. to nearly 3000 feet above the floor, which is depressed to about the same extent as that of Billy. Both the inner and outer slopes are terraced on the E., where the _glacis_ is traversed by a short, delicate, rill-like valley. There are some bright curved ridges on the floor. On the W. of Billy and Hansteen is a wide inlet of the Oceanus Procellarum, bounded by the Letronne region on the W., and on the S. by lofty highlands. On the surface, not far from the S.W. border of Hansteen, is a curious triangular-shaped mountain mass, with a digitated outline on the S., and including a small bright crater on its area. Between this and the ring- plain is a large but somewhat obscure depression, N. of which lies a rill-like object extending from the N. point of the triangular mountain to the W. wall. At the bottom of a gently sloping valley between Billy and Hansteen is a delicate marking, which seems to represent a cleft connecting the two formations. ZUPUS.--A formation about 12 miles in diameter with a dark floor, situated in the hilly region N.E. of Mersenius. FONTANA.--A noteworthy ring-plain, about 20 miles in diameter, E.N.E. of Zupus, with a bright border, exhibiting a narrow gap on the S. and two large contiguous craters on the N.W. The faint central mountain stands on a dusky interior. On the N. is a large peculiar depressed plain with a gently sloping wall, within which are three short rill-like valleys and a crater.