PYTHAGORAS.--A noble walled-plain, 95 miles in diameter, which no one who observes it fails to lament is not nearer the centre of the disc, as it would then undoubtedly rank among the most imposing objects of its class. Even under all the disadvantages of position, it is by far the most striking formation in the neighbourhood. Its rampart rises, at one point on the N., to a height of nearly 17,000 feet above the floor, on which stands a magnificent central mountain, familiar to most observers. THIRD QUADRANT EAST LONGITUDE 0 deg. TO 20 deg. MOSTING.--A very deep ring-plain, 15 miles in diameter, near the moon's equator, and about 6 deg. E. of the first meridian. There is a crater on the N. side of its otherwise unbroken bright border, an inconspicuous central mountain, and, according to Neison, a dark spot on the S. side of the floor. At some distance on the S.S.W., stands the bright crater, Mosting A, one of the most brilliant objects on the moon's visible surface. REAUMUR.--A large pentagonal enclosure, about 30 miles in diameter, with a greatly broken border, exhibiting many wide gaps, situated on the E. side of the Sinus Medii, N.W. of Herschel. The walls are loftiest on the S. and S.W., where several small craters are associated with them. A ridge connects the formation with the great deep crater Reaumur A, and a second large enclosure lying on the W. side of the well-known valley W. of Herschel. At the end of a spur on the S. side of the great crater originates a cleft, which I have often traced to the N.W. wall of Ptolemaeus, and across the N. side of the floor of this formation to a crater on the N.E. quarter of it, Ptolemaeus _d_. There is a short cleft on the W. side of the floor of Reaumur, running from N. to S. HERSCHEL.--A typical ring-plain, situated just outside the N. border of Ptolemaeus, with a lofty wall rising nearly 10,000 feet above a somewhat dusky floor, which includes a prominent central mountain. Its bright border is clearly terraced both within and without, the terraces on the inner slope of the W. wall being beautifully distinct even under a high light, and on the outer slope are some curious irregular depressions. On the S.S.E. is a large oblong deep crater, close to the rocky margin of Ptolemaeus, and a little beyond the foot of the wall on the N.W. is a smaller and more regular rimmed depression, _b_, standing near the E. border of the great valley, more than 80 miles long, and in places fully 10 miles wide, which runs from S.S.W. to N.N.E. on the W. side of Herschel, and bears a close resemblance to the well-known Ukert Valley. Herschel _d_ is a large but shallow ring-plain on the E. of Herschel, with a brilliant but smaller crater on the W. of it.