172 PETRIFACTIONS AND THEIR TEACHINGS. CHAP. III. 



ten feet in length ; others are twice as large, and indicate 

 reptiles eighteen or twenty feet long. 



It is not unusual to find specimens of these teeth partly 

 decomposed, and disclosing the successional germ ; proving, 

 that as in the crocodile, the tooth is composed of a series of 

 cones enclosed within each other, the outer or old crown 

 being burst by the pressure of the upward growth of the 

 included one. Hence, at whatever age the tooth of a crocodile 

 is removed, we find, either in the socket, or in the cavity of 

 the old tooth, a smaller cone ready to supply the place of the 

 latter, when broken or destroyed. This succession is very 

 frequently repeated, and it is from this cause that crocodilian 

 teeth in a fossil state are always so sharp and well defined, for 

 they are as perfect in the adult and aged animals as in the 

 young state. 1 



DERMAL BONES OF GONIOPHOLIS. (Lign. 40.) The most 

 remarkable character in the interesting specimen we are now 

 examining is the dermal cuirass, of which the remains, con- 

 sisting of osseous scutes, are scattered promiscuously over 

 both blocks of stone, some having the inner, and others 

 the external surface exposed. Several of these dermal 

 plates are entire (one is represented in Lign. 40) ; they are 

 six inches in length, and two and a-half in width. Frag- 

 ments of these scutes are often found in the Wealden 

 strata ; anil the earliest specimens I collected, from the 

 resemblance of their corrugated surface to that of the costal 

 plates of the carapace of 'the soft-skinned turtles (Trionyces), 

 were figured and described as such in my " Fossils of 

 Tilgate Forest," PI. VI. fig. 8 ; that opinion being sanctioned 

 by Baron Cuvier, who, with his characteristic liberality and 

 kindness, sent me models of the eocene turtles of Paris, for 

 comparison. The occurrence of similar scutes associated 

 with crocodilian bones in the Swanage specimen, first led 

 me to suspect their true character, which became manifest 

 on clearing out a perfect specimen : their nature I will briefly 

 explain. 



In the loricated tribe of reptiles, as the Crocodiles, the 

 external integument encloses numerous bony scutes, or scut- 



1 There were a considerable number of teeth of crocodilian reptiles 

 from the Wealden in my collection, but I do not know in what part of 

 the Museum they are placed. 



