Old Ivory, (16) spheres, African

I aquired 16 solid ivory balls, 15oz in weight, each. These are very old. I bought them from a Purdue Professor, retired, in his 90's, who purchased them from another Purdue Professor, when he first started at Purdue. The Original owner, a professor of Archeology, obtained them, when he spent time in Africa, poss. northern half, before he joined Purdue, as a young man. I know the ivory has been in posession of either man for a total of 116+ years.

I am having diffuculty uploading the photo, to share. A few of the balls (3) have lines on the surface, but most are smooth. Several are a light cream color, the rest are lighter shades to almost white.

I am looking to identify what they were used for, a game, to crush grain, or ? and I would like to have a value appox. placed on them as individual items, or appraisal of a single ball. The circumfrance is measured at 7 inches.