SABINE.—­The more westerly of a remarkable pair of ring-plains, of which Ritter is the other member, situated on the E. side of the Mare Tranquilitatis a little N. of the lunar equator.  It is about 18 miles in diameter, and has a low continuous border, which includes a central mountain on a bright floor.  From a mountain arm extending from the S. wall, run in a westerly direction two nearly parallel clefts skirting the edge of the Mare.  The more southerly of these terminates near a depression on a rocky headland projecting from the coast-line, and the other stops a few miles short of this.  A third cleft, commencing at a point N.E. of the headland, runs in the same direction up to a small crater near the N. end of another cape-like projection.  At 8 h. on April 9, 1886, when the morning terminator bisected Sabine, I traced it still farther in the same direction.  All these clefts exhibit considerable variations in width, but become narrower as they proceed westwards.

RITTER.—­Is very similar in every respect to the last.  A curved rill mentioned by Neison is on the N.E. side of the floor and is concentric with the wall.  On the N. side of this ring-plain are three conspicuous craters, the two nearer being equal in size and the third much smaller.

SCHMIDT.—­A bright crater at the foot of the S. slope of Ritter.

DIONYSIUS.—­This crater, 13 miles in diameter, is one of the brightest spots on the lunar surface.  It stands on the E. border of the Mare, about 30 miles E.N.E. of Ritter.  A distinct crater-row runs round its outer border on the W., and ultimately, as a delicate cleft, strikes across the Mare to the E. side of Ritter.  Both crater-row and cleft are easy objects in a 4 inch achromatic under morning illumination.

ARIADAEUS.—­A bright little crater of polygonal shape, with another crater of about one-third the area adjoining it on the N.W., situated on the rocky E. margin of the Mare Tranquilitatis, N.E. of Ritter.  A short cleft runs from it towards the latter, but dies out about midway.  A second cleft begins near its termination, and runs up to the N.E. wall of Ritter.  E. of this pair a third distinct cleft, originating at a point on the coast-line about midway between Ariadaeus and Dionysius, ends near the same place on the border.  There is a fourth cleft extending from the N. side of a little bay N. of Ariadaeus across the Mare to a point N.W. of the more northerly of the three craters N. of Ritter.  At a small crater on the S. flank of the mountains bordering the little bay N. of Ariadaeus originates one of the longest and most noteworthy clefts on the moon’s visible surface, discovered more than a century ago by Schroter of Lilienthal.  It varies considerably in breadth and depth, but throughout its course over the plain, between Ariadaeus and Silberschlag, it can be followed without difficulty in a very small telescope.  E. of the latter formation, towards Hyginus (with which rill-system it is connected), it is generally