Shrimps, Prawns and Lobsters

Most Americans use the name shrimp to include what are, in British usage, both shrimp and prawns. I say most, because I am told that at San Francisco, for example, something close to the British terminology is employed. The confusion here seems to be inevitable, since these names cut across the scientific classifications and cannot be reconciled with them or with each other. The difficulty, and the subsidiary question whether the plural of shrimp is shrimp or shrimps, can only be acknowledged, popular usage being too well established to permit any remedy.