Anthobothrium auriculatum (Rud.) is often referred to as ‘an insufficiently known species’. Southwell (1925) states that ‘all that is known about this doubtful species is contained in Rudolphi's brief description, which is quite insufficient to diagnose the species with, certainty’. Rudolphi (1819) first described it as Bothriocephalus auriculatus from Torpedo marmorata Risso; it is possible that this brief and inadequate description included several species. Leuckart (1820) described what has since been regarded as the same species under the name of Bothriocephalus flos from Carcharinus glaucus (L.), Bremser (1824) gave a brief account of Bothriocephalus auriculatus, and Zschokke (1888) gave a somewhat fuller account of Anthobothrium Auriculatum from Torpedo marmorata. As far as can be judged all these forms are synonymous. Diesing (1850) described what he thought to be Rudolphi's species, placing it in the genus Tetrabothrium; he obtained it from Torpedo marmorata Risso, Hexanchus griseus (Gm.), Carcharinus glaucus (L.), Squatina squatina (L.), and Raja calvata L. It has been pointed out by several writers that Diesing's Tetrabothrium auriculatum does not agree with Anthobothrium Auriculatum (Rud.), because, among other things, the genital pores in the former are anterior and in the latter posterior. Southwell (1925) states that Beauchamp is of the opinion that Tetrabothrium auriculatum Dies, is synonymous with Phyllobothrium gracile Wedl., an idea which is now generally accepted. Joyeux & Baer (1936) recorded Anthobothrium Auriculatum (Rud.) fairly frequently in a number of host fishes, namely, Mustelus mustelus (L.), Scyliorhinus caniculus (L.), Lamna cornubica (Gm.), Eugaleus galeus (L.), Squatina squatina (L.), Carcharias glaucus (L.), Torpedo marmorata Risso, and Raja clavata L. They, too, refer to the species as imperfectly known, and suggest that it might be synonymous with some other species of the same genus. In view of the lack of an adequate description of Anthobothrium Auriculatum it was felt that an account of its anatomy would render future identification of the species simpler and would settle the question as to whether or not it was synonymous with some other known species.