A HISTORY OF STAFFORDSHIRE which are provisionally assigned by Mr. Ward to the species known as Pteroplax cornuta, typically from the Northumberland Coal-field. Of the fishes of the Coal Measures of the county, by far the most interesting is a species of shark of the genus Edestus, the only British representative of its kind at present known. For many years certain remarkable bodies, somewhat resembling a large watch-spring armed on the convex side with teeth, have been known from the Carboniferous and Permian rocks of various countries : the most nearly complete coming from Russia. There has, however, been much uncertainty as to their true nature. At first they were supposed to be the fin-spines of fishes ; but the aforesaid Russian specimens clearly showed that they belong to the front of the jaws of sharks, and that they are true teeth, which are mounted upon their supporting bases in such a manner as to form a spiral. Hence the name of spiral-sawed sharks for the group to which they pertained. For a long time this group was known only from North America, Australia, Japan, and Russia ; the type genus being Edestus. Mr. E. T. Newton, in the Quarterly Journal of the Geological Society, has, however, described part of the ' saw ' of one of these remarkable sharks from a marine band in the Coal Measures of Nettlebank, North Staffordshire, giving the name of Edestus triserratus to the species it represents. Of the primitive group of shark-like fishes known as Ichthyotomi, and characterized, among other features, by the exceedingly imperfect calcification of the spinal column and the long-jointed axis of the pectoral fins, there are several Staffordshire representatives, belonging to the family Pleuracanthidae. Of these, the species P/eu; acanthus laevissimus is typified by a fin-spine from Staffordshire, and is known to occur in the Coal Measures of the southern half of the county and at Longton. The second species, P. cylindricus, which occurs both at Longton and Fenton, and is also known by the spines, does not appear to have been originally named from Staffordshire specimens. The genus Diplodus takes its name from having been founded on peculiar two-pronged teeth, which may really belong to Pleur acanthus. The species D. gibbosus was established on the evidence of teeth of this type from the Coal Measures of Silver- dale, in South Staffordshire, but it also occurs at Longton. Most of the other Staffordshire shark-like fishes (Elasmobranchii) belong to the existing group Selachii, although chiefly to extinct families. In the family Petalodontidae, characterized by the teeth being so much reflexed and thickened that in some cases they almost assume a crushing type, we have in the first place remains of the two common Carboniferous species Janassa linguaeformis and y. clavata from the Coal Measures of the county. To the same family belong the species Ctenoptychius apicalis. from Silverdale, Longton, Fenton, and Harecastle, and Callopristodus pectinatus, from Fenton, neither of which is, however, typically from the county. On the other hand, Helodus simplex and Pleuroplax rankinei^ belong to another family, the Cochliodontiae, a specialized ancestral type of the 15 Vol. Ix, i (1904). 36
