EXTRINSIC CHARACTERS PROGRESSIVELY MODIFIED. 35 1 



B. The Goniatitic Type of Suture. In the Goniatites we 

 find the suture lobed, forming rounded or bluntly angular 

 curvatures ; these curvatures in the simplest stage of the pro- 

 toconch are arched forward at the siphonal side (Fig. 112, 

 <z, b). In the growth of the individual, as well as in the dif- 

 ferent genera or subgenera of Goniatitidae, the lobation never 

 exceeds the repetition of these forward and backward curva- 

 tures of the suture. The multiplication of the curvatures is 

 accomplished by the infolding of the node of each curve (Fig. 

 112, d, e, f, g, and Fig. 113). 



This constitutes the Goniatitic type of suture, and consists, 

 with all its complexity and variation, of a system of curva- 

 tures forward and backward ; the forward curvatures (upward 

 in the figure) are called saddles, the backward curves (down- 

 ward in the figure) are the lobes. 



The various modifications of this type of suture are pro- 

 duced by different degrees of division of the lobes and saddles 

 in different parts of the circumference of the whorl. This 

 kind of bending of the suture may be called lobation of the 

 suture, and may be defined as the type of suture formed by 

 the primary crimping of its edges. 



C. The Ceratitic, Helictitic, and Medlicottian Types of 

 Suture. The primary lobes and saddles may be again 

 crimped so that the lobes are cut by a series of lesser lobes, 

 the saddles are dentate by secondary slits, or the sides of the 

 curves connecting the lobes and saddles are secondarily lobed ; 

 this modification constitutes a secondary system of lobation 

 of the suture ; and there are three stages of this mode of 

 crimping of the edge of the septum. 



FIG. 119. Suture of Medlicottia pritnas. (After Zittel.) 



I. The Ceratitic type, in which only the lobes (L, /, a/ l9 

 al^ of Fig. 1 14) or the backward curves of the septum edge 

 are secondarily crimped. 



