Some trematodes from Clarias spp. in the Rhodesias, including Allocreadium mazoensis n. sp. and Eumasenia bangweulensis n. sp., and comments on the species of the genus Orientocreadium Tubangui, 1931. Proceedings of the Helminthological Society of Washington, 29 1962: 103-115. 105 [Zoological Record Volume 99]