PLATE LI. 



Fig. Page. 



1-3. Ptychodus decurrens, Agassiz; associated teeth of paired (1,2) and 

 lower middle (3) rows, crown-views, the crown of the first also in 

 outline-section (la), nat. size. — Turonian zone; near Lewes. B. M. 

 no. P. 5393. 244. 



4-6. Ditto; set of upper teeth united in natural order by iron pyrites, 

 oral view, nat. size, one middle tooth being drawn separately in 

 crown-view (5) anil side view (5a), and two inner paired teeth in 

 front view (6). -Zone of Holaster subglobosus ; G-lynde, Sussex. 

 Sedgwick Museum, Cambridge. Rows numbered o' to iv\ 243. 



7. Ditto; lower middle tooth, crown-view, with outline-sections, transverse 



(7") and longitudinal (7b), nat. size. — Chalk; Kent. B. M. no. 

 43096. 241. 



8. Ditto; large, irregularly-developed upper inner paired tooth, crown- 



view, n;it. size.- Zone of Holaster subglobosus; Burham, Kent. 

 B. M. no. 32748. 242. 



9-12. Ditto; set of upper teeth united in natural order in chalk, oral view, 

 nat . size, one middle tooth being drawn separately in crown-view 

 (10), a tooth of the inner paired row being separately shown in 

 crown-view (1 1), side view (11 a), front view (11^), and from below 

 (1 1 c), also a tooth of the fourth lateral row in crown-view (12). — 

 [bid. (x. E. Dibley Collection (B. M. no. P. 10336). Lateral rows 

 numbered i' to iv'. 242. 



13. Ditto; small smooth tooth, var. levis, in crown-view and (l ; 5") outline- 



section, nat. size. — Zone of Holaster subglobosus; Mine Hell Hill, 

 Burham, Kent. S. .1. Hawkins Collection (B. M. no. I'. 6524). 240. 



14. Ditto; small tooth of similar variety, in crown-view and (1 1- a) outline- 



section, nat. size. — Zone of Holaster subglobosus; Dover. I>. M. 



no. P. 51. 240. 



