PTYCHODUS. 



241 



loc. cit., 1894), but, as suggested by Dibley {Joe. eit., 1911), they may best be 

 regarded as representing a variety of P. decurrens. 



Tig. 76. Ptychodvs decurrens, Agassiz ; associated set of teeth of both jaws, mostly in original order, nat. 

 size.— Chalk j near Brighton. Sussex. Willett Collection, Brighton Museum, no. 210a. o, Teeth of lower 

 middle row; i, n, teeth of lower first and second paired rows; o', tooth of upper middle row; i'-iv', 

 teeth of upper first to fourth paired rows. From Quart. Journ. Geol. Soc, vol. xliii (1887). 



Other teeth with typical coronal markings, such as the lower median tooth 

 shown in PL LI, fig. 7, have the marginal area relatively wide, especially in front. 



31 



