Following is an image of the page for Shumsk in the Wojewodztwo Wolynskie (Volhynia Province) Business Directory of 1923, which lists both Jews and non-Jews. The type of business and its location is listed after each name. The original directory is in both Polish and French; occupational names have been translated from the French. Surnames are given in their Polish spellings exactly as they appear in the directory.
For those unfamiliar with Polish spellings, just follow these rules of pronunciation: Polish C is pronounced like English TZ. Polish CZ is pronounced like English CH. Polish J is pronounced like English I. Polish SZ is pronounced like English SH. Polish W is pronounced like English V.
Thus, the name spelled "Kac" in Polish is equivalent to the English "Katz." Similarly, "Szmulowicz" would be written "Shmulovich" in English.
(My thanks to the Tuchin shtetlinks site for this information)