This paper considers a
family of ∗-subalgebras of a semisimple H∗-algebra A. For 0 < p ≦∞ a nonnegative
extendedreal value |a|p is associated with each a in A; then the p-class Ap is defined
to be {a ∈ A : |a|p< ∞}. If 1 ≦ p ≦∞,Ap is then a two-sided ∗-ideal of A (proper
only if p < 2), and (Ap,|⋅|p) is a normed ∗-algebra. (A2,|⋅|2) is (A,∥⋅∥); and for
1 ≦ p < 2,(Ap,|⋅|p) is a Banach ∗-algebra, for which structure theorems are
given.