TypeMismatch.cs

public interface IMessage { }

public class RemoveOrderLineItem : IMessage { }

public class MessageBus
{
    public void Send(IMessage message)
    {
        //Send the message.
    }

    public void SendAll(List<IMessage> messages)
    {
        foreach (var message in messages)
            Send(message);
    }
}

...

List<RemoveOrderLineItem> removals = new List<RemoveOrderLineItem>();
removals.Add(new RemoveOrderLineItem());
removals.Add(new RemoveOrderLineItem());
removals.Add(new RemoveOrderLineItem());

var bus = new MessageBus();

bus.SendAll(removals);