§ 40. FISHES OF THE SUSSEX CHALK. 357 



Ptychodus latissimus. Mantell's South Down Fossils. Tab. xxxii. fig. 19. Agassiz 

 Poiss. Foss. Vol. iii. tab. 25. 



polygyrus. Ibid. Tab. xxxii. figs. 23, 24. 



mammillaris. Ibid. Tab. xxxii. figs. 18, 20, 25, 29. 



decurrens. 



altior. South Down Fossils. Tab. xxxii. figs. 17, 21, 27. 



Teeth, and perhaps vertebrae, of the above species, and a few ex- 

 amples of their dorsal defences, (Ichthyodorulites of Dr. Buckland,) 

 are the only remains hitherto discovered. (Agass. Poiss. Foss. Vol. 

 iii. tab. 10% 10 b .) The teeth were referred to fishes of the genus 

 Diodon, by previous authors, and the defences were called radii, or 

 fin-bones of balistes, and siluri. 



Teeth of a new species of Ptychodus (P. Mortoni) have been dis- 

 covered in the sand of Xew Jersey, United States, by Dr. Morton. — 

 (Mortons Synopsis, PL 13, figs. 1, 2.) 



Pticholus, — sppc. undetermined. Dorsal defences, and a beautiful example of a 

 fin, are represented in the Fossils of the South Downs. Tab. 

 xxxiv. fig. 8. Tab. xxxix. and Tab. xl. fig. 3. 



Galeus pristodontus. South Down Fossils. Tab. xxxii. figs. 12 to 16. Agass. 

 Poiss. Foss. Vol. iii. tab. xxvi. fig. 14. 



Notidanus m!>ro(/o«. Agass. Tab. xxxii. fig. 22. 



Lamna appendiculaia. Agass. Tab. xxxii. figs. 2, 3,. 5, 6, 9. 



acuminata. Agass. Tab. xxxii. fig. 1. 



Mantelli. Agass. Tab. xxxii. figs. 4, 7, 8, 10. 



crassissima. 



Odontapsis raphiodon. 



Spixax major. Agass. Poiss. Foss. Vol. iii. tab. 10, figs. 8, H. 



Psammodus asper. Poiss. Foss. Vol. iii. tab. 10, figs. 1, 3. 



Acrodus transversus. Poiss. Foss. Vol. iii. tab 10, figs. 4, 5. 



Gyrodus angustus. Poiss. Foss. Vol. ii. tab. 66*, figs. 14. 15. 



The above order of fishes is represented by five genera, of which 

 one, containing twelve species, is extinct. The fishes of the genera 

 Ptychodus, Galeus, and Lamna, are very widely distributed. 



Order II. — The Ganoidians, (yavos, splendour, from the brilliant 

 surface of their enamel.) These are characterized by angular scales, 

 formed of horny or bony plates, protected by a thick layer of enamel, 

 Lign. 6S, Jig. 1, p. 339. 



Macropoma Mantelli. South Down Fossils. Tab. xxxvii. and xxxviii. Agass. 



Poiss. Foss. Vol. v. tab. 60b, fig. 2. 

 Coprolites of; South Down Fossils. Tab. ix. figs. 5, 11. 



Agass. Poiss. Foss. Vol. ii. tab. 65. 



The Macropoma is perhaps the most remarkable of all the chalk 

 fishes; in most examples the membranes of the stomach are pre- 

 served. 



