PALAEONTOLOGY modern Port Jackson sharks (Cestraciontidae), characterized by the fusion of their crushing teeth into spirally twisted oblique plates. The first- named species, which is the sole representative of its genus, appears to have been founded on the evidence of teeth from Staffordshire, where it occurs at Longton, Fenton, and Silverdale, but the second seems to be typically from Northumberland. The existing Cestraciontidae have a Staffordshire representative in the form of Spbenacantbus hybodoides, a member of a widely spread extinct genus with several species. Within the county it occurs at Longton and also near Dudley. The other Staffordshire elasmobranch fish is Acanthodes ivardi, which takes its specific title from the late Mr. John Ward, of Longton, who did such good work in collecting and describing the fossil vertebrates of the county. It is a member of the Palaeozoic group Acanthodii, charac- terized among other features, by the persistent notochord, and the pres- ence of prominent dermal appendages to the gill-arches, which during life probably carried flaps of skin ; from this character the members of the group have been called fringe-gilled sharks. Acantbodes includes several other species, but A, ivardi occurs typically in the Deep-Mine Ironstone of Longton, although it is also known from the Scottish Coal- fields. A species of the allied genus Acantbodopsis from the Woodhouse Coal of the Cheadle Coalfield has been described by Dr. R. H. Traquair in the Annals and Magazine of Natural History for 1894 16 as A. microdon, on the evidence of a specimen now in the British Museum. In addition to the foregoing, certain fin or dorsal spines of sharks or chimaeroids have been recorded from the Coal Measures of the county belonging to so-called genera of which the precise systematic position cannot at present be determined. Such is Gyracanthus formosus, widely distributed in the British Coalfields, and occurring in the county at Fenton. Another type is Euctenius unilateralis, originally described from a Lanarkshire specimen. Greater interest attaches to two masses of rock discovered by Mr. John Ward in the Middle Coal Measures of North Staffordshire containing numerous species of the doubtful type long known as Listracantbus. These have been described by Dr. Smith Woodward, 17 and are made the type of a new species, Listracantbus wardi. From these specimens it appears evident that the Listracantbus spines are strangely modified dermal tubercles occurring in considerable numbers on part at least of the head and body of the fish to which they pertain. They are identical with at least some of the structures from the Coal Measures of Indiana, U.S.A., described as Petrodus. With Ctenodus cristatus and Ct. murchisoni we come to two well- known representatives of the typical genus of the Carboniferous family Gtenodontidae^ which belongs to the sub-class of Dipnoi, or lung-fishes, and takes its name from the somewhat comb-like structure of the fine ridges on the large and flattened palatal teeth. The first species is recorded from Hanley and Tunstall, and the second from the Bassey Mine Ironstone of the Middle Coal Measures. 16 Ser. 6, xiv, 372 (1894.). " Geol. Mag. (4), x, 486 (1903). 37
