Tetraphyllidean cestodes from western North Atlantic selachians with descriptions of two new species.

Rhinebothrium corymbum sp. n. is described from Dasyatis americana Hildebrand and Schroeder. Rhabdotobothrium anterophallum sp. n. is reported from Mobula hypostoma (Bancroft) representing a new family of hosts (Mobulidae) for tetraphyllideans. Both new species can be distinguished from all others by the number and arrangement of bothridial loculi, position of the genital pore, and testes number and distribution. A new host and additional data are presented for Phoreiobothrium triloculatum Linton, 1901. The validity of Caulobothrium Baer, 1948, and Rhabdotobothrium Euzet, 1953, is discussed.