Dictyocotyle coeliaca is recorded for the first time from Raja fullonica and R. batis. It is suggested that normally D. coeliaca may be restricted to waters deeper than about 50 fathoms and that this should be considered in attempts to incubate its eggs in the laboratory. No Calicotyle kroyeri were present in female R. radiata which contained eggs in their uteri and a brief account is given of the apparent differential distribution of the species in male and female rays. Up to 64 specimens of C. kroyeri per fish are recorded from the cloacae of R. radiata (previous records refer to an average of about four specimens per host). In a brief discussion of the controversial papers on these two monogeneans reasons are given for retaining the two in separate genera.I am most grateful to the following for providing excellent facilities for the work. The Director and staff, in particular Dr B. B. Rae and Dr Z. Kabata, Marine Laboratory, Aberdeen; the Director and Staff, Plymouth Marine Laboratory; Professor James Brough, University College, Cardiff; the Director, Commonwealth Bureau of Helminthology; and Mr H. Atkinson of Messrs J. Marr and Son, Fleetwood. Additional specimens were provided by Mr J. Slinn, Marine Biological Station, Port Erin, and by Mr J. W. Smith of this Bureau.