Systematic status of Tetraonchus loftusi n.sp. (Monogenoidea: Tetraonchidae) and comparative studies of T. monenteron (Wagenar, 1857) Diesing, 1858, and T. variabilis, Mizelle and Webb, 1953. Canadian Journal of Zoology, 50(11) 1972: 1489-1495. 1490 [Zoological Record Volume 109]