AutoMapper and inheritance - How to Map?

Have this scenario:

public class Base {  public string Name; }

public Class ClassA :Base {  public int32 Number;  }

public Class ClassB :Base { public string Description;}

public Class DTO {
  public string Name;
  public int32 Number;
  public string Description;
}

I have an IList<Base> my maps are:

AutoMapper.Mapper.CreateMap<IList<Base>, IList<DTO>>()
   .ForMember(dest => dest.Number, opt => opt.Ignore())
   .ForMember(dest => dest.Description, opt => opt.Ignore());

AutoMapper.Mapper.CreateMap<ClassA, DTo>()
   .ForMember(dest => dest.Description, opt => opt.Ignore());

AutoMapper.Mapper.CreateMap<ClassB, DTO>()
   .ForMember(dest => dest.Number, opt => opt.Ignore())

Mapper.AssertConfigurationIsValid(); //Is OK!

But Properties that are in ClassA Or ClassB are not mapped when I do this :

IList<DTO>= AutoMapper.Mapper.Map<IList<Base>,IList<DTO>>(baseList);

How can I do to map properties that are defined in ClasA and ClassB