A. H. Foord — Ammonites in the British Museum. 393 



beautiful species of this group is Lytoceras fimbriatum, whose regular, 

 wavy lines running across the shell make it very attractive to the 

 eye; the effect being heightened by the bold, sharp, transverse ridges 

 encircling the shell at frequent intervals, representing the former 

 "lips" of the shell. Fig. 4. (Wall-case 11.) In Macroscaphites 

 (Wall-case 3, Table-case 61) the shell is for about four convolutions 



Fig. 3. 



Fig. 4. 



Fhylloceras heterophyllum, Sow. 

 (Upper Lias.) 



Lytoceras fimbriatum, Sow. 

 (Middle Lias.) 



or whorls exactly similar in shape to a Lytoceras, when it suddenly 

 takes a direction tangential to the coiled part, and after pursuing 

 a nearly straight course for a short distance it bends back in a hook- 

 like termination (Fig. 5). In Hamites the shell is bent at both 

 ends, the apical or smaller (initial) end being again bent : thus the 

 shell has three curvatures. Owing to its slenderness the apical part 



Fig. 5. 



Macroscaphites Ivanii, d'Orb. (Lower Cretaceous.) 



of the shell is rarely obtained (Fig. 6). (Table-case 60.) Hamites 

 attains its greatest development in the Gault. In Hamulina and 

 Ptyclioceras (Neocomian and Gault) there is but one sharp bend in 

 the shell, the straight limbs in Ptyclioceras being actually in contact 

 at, and in the region of, the aperture. 



A still further departure from the typical form of the Cephalopod 

 shell is encountered in the singular genus Turrilites, which takes 



