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.

MERSENIUS.—­With its extensive rill-system and interesting surroundings, one of the most notable ring-plains in the third quadrant.  It is 41 miles in diameter, and is encircled by a fine rampart, which on the side fronting the Mare Humorum rises 7000 feet above the floor, which is distinctly convex, and is depressed 3000 feet below the region on the E., though it stands considerably above the level of the Mare.  The prominently terraced border is tolerably regular on the N.W., but on the S. and S.E. is much broken by craters and depressions, the largest and most conspicuous interrupting the continuity of its summit-ridge on the latter side.  A fine crater-row traverses the central part of the interior, nearly axially, and a delicate cleft crosses the N. half of the floor from the inner foot of the N.E. wall to a crater not far from the opposite side.  I detected another cleft on November 11, 1883, also crossing the N. side of the floor.

South of Mersenius is the fine ring-plain Mersenius d, about 20 miles in diameter, situated on the border of the Mare; and, extending in a line from this towards Vieta are two others (a, and Cavendish d,), somewhat larger, but otherwise similar; the more easterly being connected with Cavendish by a mountain arm.  One of the principal clefts of the system (all of which run roughly parallel to the N.E. side of the Mare, and extend to the Percy Mountains