Two new species of Pseudochristianella Campbell & Beveridge, 1990 (Cestoda: Trypanorhyncha) from elasmobranch fishes from the Gulf of California, Mexico.

Pseudochristionella elegantissima sp. nov. (Cestoda: Trypanorhyncha) is described from the spiral valves of the rays Dasyatis brevis (Garman, 1880) and D. longus (Garman, 1880), from the Gulf of California, Mexico. Also described is P. nudisculo sp. nov. from rays Rhinobatos productus Ayres, 1854, D. longus, Myliobatis longirostris Applegate & Fitch, 1964 and Zapteryx exasperat (Jordan & Gilbert, 1880) from the same location. The species are distinguished from one another and from the only existing species within the genus, P. southwelli Campbel & Beveridge, 1990, by differences in the arrangement of bill-hooks on the external surface of the basal swelling of the tentacle and by the number of hooks in each row of the metabasasl armature.

Viscachataenia n. g., with the redescription of V. quadrata (von Linstow, 1904) n. comb. (Cestoda: Anoplocephalidae) in Lagidium viscacia (Rodentia: Chinchillidae) from Argentina.

A new genus, Viscachataenia, is erected to accommodate the anoplocephalid cestode Cittotaenia quadrata von Linstow, 1904, based on a redescription of the species from material collected from the chinchillid rodent Lagidium viscacia in Argentina. The new genus is characterised by paired genitalia, a reticulate uterus and the vagina entering the genital atrium anterior to the cirrus-sac. Viscachataenia therefore has similarities with Monoecocestus Beddard, 1914, a genus which is common in South American rodents but which has a single set of genitalia in each segment. Cittotaenia viscaciae (Spasskii, 1951) and Bertiella findlayi Mazza, Parodi & Fiora, 1932, also from viscachas, are considered synonyms of V. quadrata.