138 PROCEEDINGS OF THE ACADEMY OF [1892. 



straight stage. It is also to be noted in this connection that some 

 other species of Baculites, as J5. ovatus Say, B. aneeps Lam., have a 

 circular or ovate cross section in the adult stage,and probably pass 

 through the same changes as the species under discussion in their 

 earlier stages up to the circular cross section but retain this circular 

 or ovate cross section in the adult. 



An examination of the suture lines as represented in PI. IX, fig. 

 9, will show quite rapid development here too, but probably not more 

 than is common to all of the Ammonitidje. As is usual the form 

 of the second suture is entirely different from that of the first. 

 The ventral lobe in the second suture is well marked, the first lateral 

 saddle is here quite broad, the first lateral lobe is acute, and a por- 

 tion of the second lateral saddle is shown. The ventral lobe of the 

 third suture is a straight line on the end ; in the fourth the narrow 

 ventral saddle, which is located over the siphuncle, first appears. 

 The lateral lobes of the third suture are rounded instead of acute as 

 in the second suture and in each succeeding suture the lobes and 

 saddles become more rounded and deeper until they are deeper 

 than broad. During this period of its development the shell may 

 be said to be in the Cloniatite stage which persists throughout the 

 spiral shell and as far as about the 30th septum, when the second- 

 ary lobes begin to appear at the ends of the lateral saddles and the 

 shell passes into what might be called the Ceratite stage. This 

 Ceratite stage then rapidly gives place to the typical Ammonite stage 

 iu which both the lateral lobes and saddles become divided at their 

 ends. PI. IX, fig. 9, illustrates the development of the suture 

 from the initial to the Goniatite stage. Its development in the Cera- 

 tite and Ammonite stages has been illustrated in my former com- 

 munication on this species already referred to above. The comple- 

 tion of the second lateral lobe and dorsal saddle has probably already 

 taken place on the surface of contact between the protoconch and 

 the first whorl as early as the second suture, though it does 

 not appear on the free surface until the sixth suture has 

 been reached. Owing to the difficulty of handling these exceed- 

 ingly minute and friable pieces of the shell broken off in displaying 

 the inner whorls and the protoconch no attempt has been made to 

 observe the form of suture on this surface of contact between the 

 inner and outer whorls, but from examining the front view of the 

 septa as they were successively exposed, it was found that the main 

 features of the lobes and saddles first develop on this surface of con- 



