is a
Lunar Crater in the southwest part of the
Moon . The northern portion of the crater is overlaid by the
Darwin Walled Plain . To the southeast is
Byrgius Crater .
The outer wall of this formation has been heavily damaged by subsequent impacts, leaving a disintegrated rim that forms a low, irregular ridge in the surface. Parts of the crater are also overlaid by ''ejecta'' from the
Mare Orientale basin to the east. The most notable feature in the interior is the tiny, bowl-shaped impact crater 'Lamarck B'. The remainder of the floor forms a rolling, uneven plain.
Attached to the southwest rim is 'Lamarck A', a large but equally disintegrated crater. 'Lamarck D' is a huge formation that lies to the west of 'Lamarck A'. However this last feature is also worn to the point where it is barely recognizable as a crater.
By convention these features are identified on lunar maps by placing the letter on the side of the crater mid-point that is closest to Alder crater.
