Notation in atomic structure In the book, The theory of atomic structure and spectra, Robert D. Cowan says that the allowed terms of $p^2$ are $^1S$, $^1D$, $^3P$ and so the possible terms of $p^2 + p\quad$ (obtained by using the vector model) are:

$$^2P^\circ,\quad ^2P^\circ D^\circ F^\circ,\quad ^{2,4}S^\circ P^\circ D^\circ 
 \tag1$$  

I am having trouble in understand the notation in $(1)$. For example  the term $^2P^\circ$ means that $s=1/2,l=1$ and $^\circ$ means odd parity, but for the term $^{2,4}S^\circ P^\circ D^\circ$, I do not know what it means. Can anyone explain me it please?
Copied table below from "Quantum chemistry", Donald A. McQuarrie, University Science Books,  2008, page 472

This illustrates the notion that $p^2$ and $p^4$ are equivalent.  



I think the 2,4 superscript in Cowan's book for $^{2,4}S^\circ P^\circ D^\circ$ is a peculiar notation of his. Most other books seem to presume the reader knows the equivalency.