A. H. Foord — Ammonites in the British Museum. 395 



gradational series connecting the Goniatites with the Ammonites. 

 (Table-case 69.) 



The principal feature observable in the Amaltheid^ is the heel or 

 projecting edge of the outer border (periphery) of the shell, which 

 is prolonged beyond the margin of the aperture in the form of 

 a long narrow process. In Amaltlieus margaritatus (Middle Lias) 

 the keel is prominent and beautifully sculptured, resembling the 



Fig. 9. 



Baculites anceps, Lam. (Upper Cretaceous.) 



strands of a miniature rope. Cardioceras cordaium (Oxford Clay) 

 is one of the most highly ornamented of Ammonites, having a series 

 of numerous sharp ribs upon the sides of the shell, which, in passing 

 over the periphery, form a series of fine crenulations (Fig. 10). 

 ScMoenbachia varians (Lower Chalk) has strong and knotted ribs. 

 (Wall-cases 5, 9, 11; Table-cases 62-69.) 



The family of the ARiETiDiE embraces a large number of Am- 

 monites which at first sight appear to be only remotely related, 

 nevertheless a careful study of their development has led to their 



Fig. 10. 



Cardioceras cordatum, Sow. (Oxford Clay.) 



being grouped together. Among the most familiar members 

 of this large group are the following, viz. : Psiloceras planorbe, 

 which gives its name to the " zone of Ammonites planorbis " of the 

 Lower Lias, and at the same time marks the first occurrence of 

 Ammonites in British rocks ; Arietites BucJclandi (A. Bucklandi 

 zone) ; Arietites obtusus, Fig. 11 (_A. obtusus zone) ; and Oxynoticeras 

 oxynotum (A. oxynotus zone). 



The shells in this group are flattened in form, and the whorls 

 usually only slightly embracing, and generally numerous (see Psilo- 

 ceras planorbe, e.g.). Oxynoticeras oxynotum is remarkable for the 



