LI^NEAX SOCIETY Or LOXDOX. 



35 



paired series along the symphysis of the jaw. Each of these 

 teeth is so much narrower in front than behind, that there must 

 have been very few in succession during tlie individual lifetime. 

 The dentine is coarsely tubular and uniform throughout the 

 crown of the tooth. In very young individuals tlie teeth of 

 the right and left sides are proved to differ a little in width ; and 

 in adult individuals all the teeth of one side, so far as known 

 both in Europe and America, are very much wider than those of 



Eiff. 3. 



%■. 



M^. 



Diagraiiunatic transverse section of jaws with teeth of Janassa bituminusa 

 from the Lower Permian of Tliuringia, about nat. size (after Jaekel). Six 

 discarded siiccessioLial teeth are seen resting beneatli tlie tootb which is in 

 use both in the upper {Ok.) and iu the lower (Uk.) jaw; while another 

 successional tooth, above (Ej.) and below (Eff.), is shown ready to come 

 into place in due time. Qi'ff. and U/>(/. mark the articular ends of 

 the jaws. 



the other siile. The dentition must therefore have exhibited the 

 unusual asymmetry represented in fig. 4, and this asymmetry 

 would be reversed iu the two jaws. 



The Ui)per Devonian and Carboniferous Copodontidie, which 

 are also known only by their teeth, seem to approach the 

 Chimoeroids more closely tluin tlie Psammodoutidoe. In them the 

 teeth are bilaterally symmetrical, arranged along the symphysis of 

 the jaw in a single autero-posterior series, and embedded in a 

 greater or less extended plate of highly vascular and softer 

 dentine. The succession of these teeth in the typical Carboni- 

 ferous genus Coporlus is very difficult to understand ; and in the 



d2 



