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 



