314 PALAEONTOLOGY OF ILLINOIS. 



the several rows, as mentioned in connection with those of the posterior 

 portion of the jaw, present but slight differences to one another, until 

 reaching the extreme anterior rows, where they appear to assume irreg- 

 ularities which give rise to considerable diversity, especially in the pre- 

 sence in the extreme anterior row of minute, nearly circular teeth, 

 which exhibit in the form of the crown and its sculpturing strong like- 

 ness to Petrodus ; besides other scute-like and irregular forms, the posi- 

 tion of which is not so clear, more particularly noticed further on. 



.The single ramus above described shows about four hundred and fifty 

 individual teeth, and in its perfect state there were probably not less 

 than five hundred, or one thousand teeth for the entire mandible. 



Eemarkable as this specimen is, showing as it does the nearly com- 

 plete details of the dentition of the jaw, it unfortunately reveals no 

 facts relative to that of the maxillaries or upper jaw, detached teeth of 

 which, for all the aids afforded by the example before us, might be mis- 

 taken for representatives of distinct specific forms. But it is a matter 

 of much importance to the student of these remains, the discovery by 

 Prof. Todd, in the shales of about the same stratigraphic horizon of the 

 Upper Coal Measures of south-western Iowa, of a mass of detached 

 teeth, occurring within so limited a compass and under conditions which 

 leave little room to doubt but that they constituted the dental remains 

 of a single fish. Prof. Todd obtained in all some two hundred speci- 

 mens of individual teeth, the greater number of which are quite 

 detached, though a few are still associated in rows and parts of series 

 precisely as represented in the before mentioned specimen from Kansas. 

 Unfortunately the existence of these interesting fossils was not made 

 known sufficiently early to secure the entire set, as many, in fact the 

 great majority of the teeth were lost by being concealed in the debris 

 from the quarry, from which, indeed, many of the specimens here allu- 

 ded to were rescued. Yet this collection, assuming that it represents 

 the dental armature of one and the same individual, supplies, in part 

 at least, exactly the data not exhibited in the previously noticed spe- 

 cimen, inasmuch as the same sort of teeth are found amongst these 

 Iowa specimens, besides other forms which it were difficult to account 

 for on the ground of abnormal development, but which probably per- 

 tain to the opposite or maxillary portion of the jaws. While these 

 materials afford additional data contributing to a more extended know- 

 ledge of the somewhat variable dentition of this group, we are still left 

 in doubt as to the character and the extreme extent of the variableness 

 of the teeth which occupied the anterior and posterior portions of the 

 maxillaries, as the collection last referred to affords no individuals of a 

 kind of extremely acuminate teeth, examples of which have been dis- 

 covered in the Upper Coal Measures of Illinois. 



