that a formation which is thrown into such strong relief at sunrise and sunset should have been overlooked, while others hardly more prominent at these times have been drawn and described.  The outline of Cassini is clearly polygonal, being made up of several rectilineal sections.  The interior, nearly at the same level as the outside country, includes a large bright ring-plain, A, 9 miles in diameter and 2600 feet in depth, which has a good-sized crater on the S. edge of a great bank which extends from the S.W. side of this ring-plain to the wall.  On the E. side of the floor, close to the inner foot of the border, is a bright deep crater about two-thirds of the diameter of A, and between it and the latter Brenner has seen three small hills.  The outer slope of Cassini includes much detail.  On the S.W. is a row of shallow depressions just below the crest of the wall, and near the foot of the slope is a large circular shallow depression associated with a valley which runs partly round it.  The shape of the glacis on the W. is especially noteworthy, the S.W. and N.W. sides meeting at a slightly acute angle at a point 10 or 12 miles W. of the summit of the ring.  On the outer E. slope is a curious elongated depression, and on the N. slope two large dusky rings, well shown by Schmidt, but omitted in other maps.  Most of these details are well within the scope of moderate apertures.  Perhaps the most striking view of Cassini and its surroundings is obtained when the morning terminator is on the central meridian.

ALEXANDER.—­A large irregularly shaped plain, at least 60 miles in longest diameter, enclosed by the Caucasus Mountains.  On the S.W. and N.W. the border is lineal.  It has a dark level floor on which there is a great number of low hills.

EUDOXUS.—­A bright deep ring-plain, about 40 miles in diameter, in the hilly region between the Mare Serenitatis and the Mare Frigoris, with a border much broken by passes, and deviating considerably from circularity.  Its massive walls, rising more than 11,000 feet above the floor on the W., and about 10,000 feet on the opposite side, are prominently terraced, and include crater-rows in the intervening valleys, while their outer slopes present a complicated system of spurs and buttresses.  There is a bright crater on the N. glacis, and some distance beyond the wall on the N.W. is a small ring-plain, and on the S.E. another, with a conspicuous crater between it and the wall.  Neison draws attention to an area of about 1400 square miles on the N.E. which is covered with a great multitude of low hills.  E. of Eudoxus are two short crossed clefts, and on the N. a long cleft of considerable delicacy running from N.E. to S.W.  It was in connection with this formation that Trouvelot, on February 20, 1877, when the terminator passed through Aristillus and Alphonsus, saw a very narrow thread of light crossing the S. part of the interior and extending from border to border.  He noted also similar appearances elsewhere, and termed them Murs enigmatiques.