46 EXPLANATION OF 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 Chalk. 



Fig. 5. Side View of fig. 4. 



Figs. 6 — 10. Teeth of extinct fossil Sharks in the sub- 

 family of Hybodonts ; in this family the enamel is 

 plicated on both sides of the teeth. See V. L 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. L p. 289, Note. 



Fig. 14. Palatal teeth of Myliobates striatus, from the 

 London clay of Barton cliff, Hants. See V, L p. 291 . 

 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. Ichthyodorulite, 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.) 



