This book and the accompanying exhibition show facets of African art seldom seen in this country. Not only the individual works, but the nature of this collection, and the intellectual approach of its curator are new to most Americans. Few American museums have collections as large as this one, over 20,000 objects from which the 450 here were culled - and few Americans collections have such a preponderance of material documented to the earliest days of collecting and before. Above all, few museums have had the energy and the resources to publish their African collections in so thorough a fashion.