346 



GEOLOGICAL BIOLOGY. 



is, an undulating or notched suture formed of simple lobes and saddles 

 (Fig. 112). 





FIG. ii2. Development of the su- 

 ture of Goniatites diadema Goldf. 

 (After Branco.) 



D ~~MJ\f\T\l\/\w 



FIG. 114. Suture of Ceratites nodosus. 



FIG. 113. Sutures of the various tribes of 

 Goniatites. (According to the Sandberg- 

 ers.) A = Linguati, G. tuberculosis cos- 

 tatus ; B= Lanceolati, G. Becker i ; C 

 Genufracti, G. sphericus; D = Serrati, G. 

 saggittarius; .ZT=Crenati, G. intumescens; 

 F = Acutolaterales, G. terebratus ; G = 

 Magnosellares, G. retrorsus ; /z r =Nauti- 

 lini, G. subnautilinus. 



A later complication is observed in the Ceratite stadium, in which the 

 saddles remain intact while, on the contrary, the lobes are notched by 

 slight denticulations. The more elaborate differentiation is reached in 

 the Ammonite stadium, in which the lobes and saddles are gashed by 

 secondary notches in the most variable manner. 



FIG. 115. Suture of an Ammonite, Desmoceras latidorsatum. (After Zittel.) 



As the Goniatites appeared, in general, before the Ceratites, and these 

 in part before the true Ammonites, it is believed that these three genera 

 may be considered to be the three principal stadia of development of the 

 Ammonoids. This view is further confirmed by the fact that the suture 

 line of all Ammonites in the course of the first whorl passes through the 

 Goniatite stadium (Fig. 116, H to N), According to the researches of 

 Hyatt and Branco, however, the Ceratite stadium is, in general, passed 



