42 
EXPLANATION OF PLATE I. 
(Th’s Plate is presented to the Society by W. Feed, Esq., F.Gr.S.) 
Pig. 1. Platy cheer op s Richardsoni, Charleswortli; palatal portion 
of skull. London Clay, Herne Bay (Peed Collection). Fig. \a, 
Pigkt upper molar 2, three times natural size. 
Fig. 2. Ctenodus inierruptus, Barkas ; left lower tooth. Carbon¬ 
iferous Limestone, Gilmerton, near Edinburgh, x., broken anterior 
ridge. 
Fig. 3. Ptychodus mammillaris, Agassiz; lower median tooth, 
coronal aspect. Chalk, near Pochester (Peed Collection). Fig. 3». 
Ditto, transverse section of crown. 
Fig. 4. Ditto; upper median tooth, coronal aspect, associated 
with the preceding. Fig. Aa. Ditto ; transverse section. 
Figs. 5—14. Ditto ; coronal aspect of ten lateral teeth, associated 
with the preceding. Figs. Qa, la, \\a, \Aa. Ditto; transverse 
sections of dental crowns. 
Fig. 15. Ptychodus poly gyrus, Agassiz; coronal aspect of lower 
median tooth. Chalk, between Folkestone and Dover (Peed 
Collection). Fig. \ba. Ditto; transverse section of dental crown. 
Figs. 16—20. Ditto; coronal aspect of five lateral teeth, 
associated with the preceding. Fig. 16^?. Transverse section of 
dental crown. 
Unless otherwise stated, the figures are of the natural size. 
22 Affi. 90 
