The work of Hiratsuka and Cummins has much improved our understanding of the significance of pycnia in taxonomy. Previously many authors had tended to regard pycnial position, for example, subepidermal, intraepidermal, or subcuticular, as the only pycnial feature of importance in differentiating genera (e.g., Arthur, 1934; Cummins, 1959; Thirumalachar, 1961).
Source: wiktionary