The remains of fishes discovered in the Cambridge Greensand are all very fragmentary, and have not hitherto been subjected to the detailed comparison with other Cretaceous Ichthyolites which their interesting stratigraphical position renders desirable. Many specimens, however, are capable of at least generic determination, while many others are sufficiently characteristic fragments for the definition of the species. The present writer has thus been much interested during the past few years in studying collections of these fossils, and the following notes embody some of the results in reference to the ganoid fishes. The British Museum (Natural History) having recently acquired the collection made from the Cambridge Greensand by Mr. Thomas Jesson, F.G.S., nearly all the known species are now represented here; but the writer has also availed himself of the privilege of making use of the fine series in the Woodwardian Museum, Cambridge, and the Philosophical Society's Museum, York, thanks to the kindness of Professor McKenny Hughes, Mr. Henry Woods, and Mr. H. M. Platnauer. Mr. James Carter, M.R.C.S., has also kindly lent some Pycnodont jaws from his private collection