394 A. H. Foord — Ammonites in the British Museum,. 



the form of a Gasteropod shell (Fig. 7). The naouth or aperture is, 

 however, turned towards the left-hand side, or, in other words, the 

 shell is " sinistral." Turrilites is found exclusively in Cretaceous 

 rocks. (Wall-case 3, Table-case 60.) Eelicoceras is coiled like 

 Turrilites, but the whorls are disconnected. In Heteroceras the last 



Fig. 6. 



Samites elegans, d'Orb. (Cretaceous.) 



whorl is detached (Fig. 8). Both are Cretaceous genera. (Table- 

 case 57.) In Bacidites (Cretaceous) the shell is perfectly straight, 

 except in the earliest or embryonic stage of its development, in 

 which it is coiled. It occurs in vast numbers in the Danian (Upper 

 Continental Chalk) of the North of France, whence the name BacuJite 

 Limestone given to those beds (Fig. 9). (Wall-case 3, Table-case 60.) 

 The next group, Ptyuhitid^, consists for the most part of 

 Triassic genera, but its earliest representatives come from the 



Fig. 7. 



Fig. 8. 



Turrilites catenatus, d'Orb. 

 (Gault.) 



Heteroceras Emerici,, d'Orb. 

 (Cretaceous.) 



Permian rocks of Sicily. Ptyclntes and Gymnites from the Alpine 

 Trias are among the best known genera. Daraelites of the Permian 

 of Sicily is specially interesting from the fact that its sutural 

 c'haracters resemble those of some of the Goniatites, and taking 

 the Ptychitid^ as a whole it is considered that they present a 



