The life-cycle of the digenetic trematode, Proctoeces maculatus (Looss, 1901) Odhner, 1911 [Syn. P. subtenuis (Linton, 1907) Hanson, 1950], and description of Cercaria adranocera n. sp. - Stunkard, H. W.; Uzmann, J. R. (Biological Bulletin, 1959)