74 CEPHALOPODA. 



result of this is that the " sutures " or edges of the septa 

 appear on the surface of the shell in the form of angulated, 

 lobed, or foliaceous lines (fig. 461). 



The angulated or digitated portions of the suture which 

 are directed inwards, away from the mouth of the shell, are 

 called the " lobes." The elevations between the " lobes," 

 which pomt towards the mouth of the shell, are called the 

 "saddles." These parts have the following arrangement 

 (fig. 461) : In the middle of the back or convex surface of 

 the shell, traversed by the siphuncle, is a single unpaired 

 lobe M^hich is termed the " dorsal lobe " (d). The lobe on 

 each side of this is the " lateral-superior " lobe (l). The lobe 

 next to this again is the " lateral-inferior " lobe (e) ; and 

 the lobes which follow this (of a variable number) are the 

 " auxiliary " lobes (a^, a^, a^, a*). Lastly, there is a 

 second unpaired lobe immediately opposite to the dorsal 

 lobe, placed upon the concave side of the shell, and termed 

 the " ventral " lobe. The " saddles " are similarlv sub- 



Fig. 401. — One half of the suture of AmiiwaUes Tritdlii. d, Dorsal lobe, traversed by 

 the siphuncle ; l. Lateral-superior lobe ; e, Lateral-inferior lobe ; a1, a2, a3, a'*, Auxiliary 

 lobes ; sd, Dorsal saddle ; sl. Lateral saddle ; si, s"-, s3, s^, Auxiliary saddles. 



divided. Between tlie dorsal and lateral - superior lobes 

 comes the " dorsal saddle " (sd). Xext to this, between 

 the superior-lateral and inferior-lateral lobes, is placed the 

 " lateral saddle " (sl) on each 'side ; and this is followed 

 by a variable number of " auxiliary saddles " (s^, s^, s^, s*). 

 The aperture of the shell in the Ammonitidcc is com- 

 monly furnished with lateral processes of greater or less 

 length ; and in some, if not in all cases, it was further pro- 



