4G EXPLANATION OP PLATE 27''. 
Fig. 1. Psammodus, from Mountain limestone, Bristol. 
Fig. 2. Orodus, from the same. 
Fig. 3. Acrodus, from the Lias, Lyme Regis. 
Fig. 4. Ptychodus, (upper surface) from the Clialk. 
Fig. 5. Side View of fig. 4. 
Figs. G — 10. Teeth of extinct fossil Sharks in the sub- 
family of Ilybodonts ; in this family the enamel is 
plicated on both sides of the teeth. See V. 1. p. 288, 
Note. 
Fig. 6. Side view of tooth of Onchus, from the Lias at 
Lyme Regis. 
Fig. 7. Front view of the same. 
Figs. 8. 9. 10. Teeth of Hybodonts, from the Oolitic slate 
of Stonesfield, Oxon. 
Figs. 11. 12. 13. Fossil Teeth of true Sharks in the 
Squaloid division of that family, having the Enamel 
smooth on the outer side. From the Chalk and 
London clay. See V. I. p. 289, Note. 
Fig. 14. Palatal teeth of Myliobatis striatus, from the 
London clay of Barton cliff, Hants. See V. I. p. 29 1 . 
Much of the enamel is worn away by use, as fre- 
quently happens in the tongue and palatal bones of 
living Rays. (Original.) 
C. Petrified remains of an extinct Genus of Shark. 
Fig. 1. Jaw of Hybodus reticulatus, from the Lias at 
Lyme- Regis, (scale one half.) Many of the Teeth 
retain their place on the margin of the bone. The 
granulated structure of bone is distinctly preserved. 
(De la Beche.) 
Fig. 2. Teeth selected from the Jaw last figured. Nat. 
size. 
Fig. 3. Icthyodorulite, from the Lias at Lyme Regis, 
being the Dorsal spine of Hybodus incurvus, set 
with teeth-like hooks, to suspend the membrane of 
the dorsal fin. (De la Beche.) 
