Coal; its history and uses . h has been established in Dipterus teeth have not, it is true, been actually seen, butDr. Giinther has figured a Dipterus skull which showsquite unmistakably the two small sockets, and theseexactly where the vomerine teeth ought to be. Dipterusis fuither distinguished by the form of the paired fins,which are long and slender, covered along the centre witha thin, pointed strip of scales and fringed by fin-rays. ANIMALS OF THE COAL MEASURES. 139 Agassiz lias described in his book on Fossil Tisbessome large and peculiar teeth found in the Trias ofGermany and
Coal; its history and uses . h has been established in Dipterus teeth have not, it is true, been actually seen, butDr. Giinther has figured a Dipterus skull which showsquite unmistakably the two small sockets, and theseexactly where the vomerine teeth ought to be. Dipterusis fuither distinguished by the form of the paired fins,which are long and slender, covered along the centre witha thin, pointed strip of scales and fringed by fin-rays. ANIMALS OF THE COAL MEASURES. 139 Agassiz lias described in his book on Fossil Tisbessome large and peculiar teeth found in the Trias ofGermany and also in a conglomerate or bone-bed ofabout the same geological age, which occurs at Aust Cliffon the Severn. These teeth were triangular or semi-ovalin outline, with blunt transverse ridges and a wavy were at first believed to belong to Sharks, and werenamed Ceratodus or horn-tooth on account of their pro-jecting cusps. Agassiz conjectured very acutely (fornone of these teeth were united, or retained more than a. Fig. 26. Under surface of skull of Dipterus. trace of the attached bone) that they had been set iuopposed pairs in the mouth, and that the ridged or wavymargin had been outermost. These suppositions havebeen amply confirmed. In 1870 Mr. Gerard Krefft founda quite similar fish living in the fresh waters of Queens-land. Many specimens have now been examined byzoologists, and it is placed beyond doubt that the genusCeratodus still survives. The crushing plates are curi-ously like the fossil teeth of the Trias, and set as Agassizhad supposed, one pair in the roof of the mouth, another inthe lower jaw. The recent Ceratodus moreover exhibitsa pair of cutting vomerine teeth, in front of the palatalplates, just as in Dipterus and probably also in Ctenodus. 140 COAL. There are thus three distinct forms, belonging to three ormore geological periods, which resemble each other in avery exceptional arrangement of teeth. The resemblancedoes not end here. Ceratodus has p
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