COLLECTION AND PRESERVATION OF FOSSILS 353 



sealing wax, gutta-percha and the various compositions 

 used by dentists for moulding the teeth and palate. 



The various methods so far described give some idea 

 of the most frequent and general forms of palaeon- 

 tological technique. Other special methods can only be 

 mentioned, such as the delicate methods employed by 

 Norman Glass and others for exposing the brachial 

 spirals of brachiopods, the methods of exposing, tracing, 

 and reproducing the suture -lines of ammonoids (see 

 Frontispiece), the making of serial sections of solid fossils 

 at regular intervals and constructing from them enlarged 

 models of the internal structure. The accurate measure- 

 ment of fossils by means of sliding callipers is a very 

 necessary process in the identification of species and the 

 tracing of gradual evolution. 



