INDIVIDUAL AND PALJEONTOLOGICAL EVOLUTION 259 



undulated lobes or bands, without secondary 

 denticulations. All forms of the saddleless or 

 broad-saddled animals in which the sutures in the 

 adult remain at this slight degree of complication, 

 constitute the group of Goniatites, which are peculiar 

 to Primary times. This great family presents 

 very varied types, of which each one marks an 

 arrest in one of the phases of development through 

 which pass the Ammonites properly so called. 

 In these, the suture line does not remain in this 

 simple state ; it is complicated by the multipli- 

 cation of the bands and lobes, and by the sub- 

 division of these parts. In the Ceratitce of the 

 Trias the first degree of complication appears, 

 in which the bands or convex parts remain in- 

 tact, while the lobes or concave parts are slashed 

 with fine dentelations. Lastly, in most Ammonites, 

 the bands and lobes are not only dentelated, 

 but subdivided ad infinitum, giving the type of 

 spangled partition, reminding one of the manifold 

 crimpings of a parsley leaf. 



One of the most interesting results of these 

 studies has been the established fact that the 

 Ammonites with, in the adult stage, the most 

 complicated compartments successively present first 

 the Goniatite stage, and then sometimes the Ceratite 

 before reaching the Ammonite stage, which is 

 acquired at a diameter of three to four millimetres 

 at most. Hyatt and Branco have shown, however, 

 that the Ceratite stage is generally passed over, and 

 that the suture of the Goniatite type passes direct 

 to the Ammonite stage. 



Modem palaeontologists make use with great 



