Lamarck is a crater

Impact crater

In the broadest sense, the term impact crater can be applied to any depression, natural or manmade, resulting from the high velocity impact of a projectile with a larger body...

 in the southwestern part of the Moon

Moon

The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

. The northern portion of the crater is overlain by the walled plain Darwin

Darwin (lunar crater)

Darwin is a lunar crater of the type categorised as a walled plain. It lies in the southeastern part of the Moon, and is sufficiently close to the limb to appear significantly foreshortened when viewed from the Earth. Attached to its southern rim is Lamarck...

. To the southeast is Byrgius

Byrgius (crater)

Byrgius is a lunar crater located in the western part of the Moon, near the limb. As a result Byrgius appears strongly oval in form due to foreshortening. To the northwest is the nearly ruined crater Lamarck. The rim of Byrgius is worn and eroded, with Byrgius A overlying the eastern rim and...

.

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 overlain by ejecta from the Mare Orientale

Mare Orientale

Mare Orientale is one of the most striking large scale lunar features, resembling a target ring bull's-eye. Located on the extreme western edge of the lunar nearside, this impact basin is difficult to see from an Earthbound perspective.Material from this basin was not sampled by the Apollo program...

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 southwestern 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.

Satellite craters

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 Lamarck.

Lamarck	Latitude	Longitude	Diameter
A	25.2° S	70.8° W	51 km
B	22.8° S	69.7° W	7 km
D	25.0° S	74.1° W	131 km
E	26.8° S	75.7° W	9 km
F	27.0° S	73.9° W	9 km
G	27.1° S	72.1° W	15 km