RAMBLES AND REVERIES. 



A. communis (Fig. 17) is very plentiful in the 

 Middle and Upper Lias, and gives its name to one 

 of the Liassic zones. Its shell ornamentation 

 consists of rings, the side view showing portions of 

 these circular lines lying parallel with each other. 



A. obtusus (Fig. 24) is a characteristic fossil of the 

 Lower Lias. It has a keel on the back of the shell 

 with radiating ribs along the sides. The body cham- 

 ber is large, occupying more than one complete whorl. 



FIG. 24. 



Flo. 25. Side view. 



So far I have mentioned only Liassic Ammonites, 

 but they occur all through the Secondaries, that is> 

 the Lias, the Oolites, and the Chalk. One of the 

 commonest, as well as one of the most beautiful, of 

 these fossils is A lautm (Fig. 26), from the Cretaceous 

 series. The Gault beds in this series, seen so well at 

 Folkestone, are crowded with Ammonites of almost 

 every conceivable pattern. They vary remarkably in 

 size, some, like A. lautus, being less than half an inch 



