Hamatopeduncularia australis sp. n. and H. brisbanensis sp. n. (Dactylogyridae) are described from the gills of Neoarius australis from the tidal part of the Brisbane River, Queensland, and the former also from Moreton Bay, Queensland. H. australis differs from all other species in the genus by possessing three sclerotized ridges on the ventral surface of the peduncle and by the shape of the hamuli (anchors) and transverse bars. H. brisbanensis differs from all other species of the genus by the filamentous shape of the terminal part of the penis stylet and the unusually shaped hamuli and transverse bars. H. nengi (Tripathi, 1959) comb. n. is transferred to Hamatopeduncularia from Ancyrocephalus Creplin, 1839 and Hargitrema eilatica (Paperna, 1965) comb. n. is transferred from Hamatopeduncularia to Hargitrema Tripathi, 1959. The generic diagnosis of Hamatopenduncularia is emended. Trochopus plectropomi sp. n. (Capsalidae) is described from the gills of Plectropomus maculatus (Bloch). It differs from all other species by possessing both eight radial septa in the opisthaptor and the pore of the copulation canal adjacent to the genital pore. Pseudoleptobothrium aptychotremae gen. et sp. n. (Microbothriidae) is described from the skin of Aptychotrema banksi. It differs from the most closely related genus, Leptobothrium, by the presence of a single pore to the copulation canal. It differs from all other species in the family by the presence of an ovary which is looped around the right gut crus. This is the first record of a member of this family on a fish from the family Rhinobatidae. During an investigation into the monogenoid fauna of Australian fishes many new and previously described species were found on a wide variety of fishes. The present paper includes descriptions of new species from the genera Trochopus Diesing 1850, Hamatopeduncularia Yamaguti, 1953 and a new genus Pseudoleptobothrium. These were found respectively on Plectropomus maculatus (Bloch) the coral trout, Neoarius australis (Giinther) the blue catfish, and Aptychotrema banksi (Muller and Henle) Bank's shovel-nosed shark. The fishes were obtained from a variety of sources. Specimens of P. maculatus were speared in 10 to 15 ft of water over coral reef at Heron Island, Queensland, specimens of N. australis were caught by hook and line in the estuarine and tidal part of the Brisbane River, Queensland and specimens of A. banksi were collected from Moreton Bay, Queensland by commercial stake-netting fishermen. P. maculatus and N. australis were examined a few hours after capture. The specimens of A. banksi were transported alive to the laboratory and examined immediately after death. The monogenoid specimens were fixed both flattened and unflattened in an A.F.A. mixture Received for publication 3 March 1967. * Present address. and stained with hemalum. Some living specimens were also studied. The terminology concerning monogenoid structures is at present quite indeterminate. Hyman (1951) used morphologically precise terms to describe the genitalia in this group and her terms are generally followed in the present paper. Llewellyn (1963) gave a specific embryological definition to the main hooks of the monogenoid opisthaptor and called them hamuli. Because of this his term is used. Larval hooks are so called because they are primarily larval structures and are often lost or modified in the adult worm. All measurements are in microns unless otherwise indicated. Hamatopeduncularia australis sp. n. (Figs. 1-7) Host: Neoarius australis (Giinther), the blue catfish. Location: Gills. Locality: Tidal part of Brisbane River, Brisbane, Queensland. Material examined: Four specimens of the host were examined, one was parasitized by H. australis sp. n. Seven specimens of the parasite were examined alive and preserved; five were measured. USNM Helm. Coll. Nos.: Holotype 61289, paratypes 61290. Description With characters of the genus, body 495 to 857 long by 121 to 164 wide at ovary; two pairs of