The mummies are among 400-500 located thus far in what Egypt has dubbed the Valley of the Golden Mummies - grounds where thousands were believed entombed.

The rare limestone sarcophagus that covered Badi-Herkhib - the elder brother of a governor of Bahariya who lived around 500 B.C. - was discovered last week, allowing archaeologists to more closely study a family that ruled this part of Egypt.

''This family was so powerful, so wealthy, that they could import the limestone from about 100 kilometers [62 miles] away,'' said Mansour Boraik, a senior archaeologist overseeing the Bahariya site.

The large sarcophagus was several inches thick and weighed an estimated 15 tons.

The cemetery, covering about 2 square miles, is 235 miles southwest of Cairo. Egypt's chief archaeologist, Zahi Hawass, said the discovery of Badi-Herkhib's tomb was unexpected.

''As a matter of fact, the family tree did not mention the person we found,'' Hawass said.

He said the tomb was robbed during the Roman era.

A dozen mummies from middle-class backgrounds also were displayed in their family tomb in a different part of the burial grounds. The mummies, most of them in a deteriorated condition, were found in three burial chambers, lying in neat rows.

The mummies were part of a group of about 20 found last week. Boraik estimated the cemetery holds about 15,000 mummies.