This is the genuine, original equipment (OEM) white plastic lens for the roof mounted dome light. These commonly become brittle and discolored with age, and can also crack when improperly removed.
Datsun 280ZX, Nissan 300ZX
Datsun S130, Nissan Z31
1979, 1980, 1981, 1982, 1983, 1984, 1985, 1986, 1987, 1988, 1989