198 



THE LIAS AMMONITES. 



ium^ d'Orb. (fig. 



foliated. The Ligati are all Cretaceous forms, and Haploceras 

 from the Neooomian, is a typical species. 



18th Section. Planulati, von Buch. See p. 189 

 19th Section. Coronarii, von Buch. See p. 190. 

 20th Section. Macrocephali, von Buch. See p. 190. 



21st Section. Yiu^^ikti, d'Orbigny. Shell discoidal; formed of cylindrical whorls ; 

 often contiguous and without involution ; smooth, or ornamented transversely at regular 

 distances apart, with prominent ribs or grooves, which are the remains of a portion of 

 the mouth appendages of the species. Mouth circular. Septa symmetrical, formed of 

 lobes and saddles divided in part into pairs, always enlarged at their extremity and 

 narrow at the base ; siphonal lobe often the longest. Aegoceras fimhriatum. Sow. (fig, 85), 

 of the Middle Lias, is a good type of this group. The Fimbriati are found in the 

 Jurassic rocks and Lower Cretaceous strata. 



Fig. 84. — Haploceras ligatum, d'Orb. Fig. S5. — Aegoceras -fimbriatum, Sow. Fig. 86. — Crioceras Emerici, Leveille. 



h. Species with ramified septa ; whorls coiled spirally on the same plane, not contiguous. 



Genus Crioceras, Leveille. Animal unknown. Shell discoidal, rolled on the same 

 plane, whorls round or oval, and not contiguous. Septa transverse, divided regularly 

 into six lobes, mostly formed of single parts, the siphonal lobe excepted, and the saddles 

 formed of parts nearly always in pairs. The superior lateral lobe is longer than the 

 siphonal lobe. The lobes and the saddles are narrow at the base and much enlarged at 

 their extremity. Siphuncle continuous, always marginal. Two thirds of the last whorl 

 formed the dwelling chamber of the animal. Eound in the lower strata of the Cretaceous 

 formation. Crioceras Emerici (fig. 86) is a typical form. 



Genus Scaphites, ParJdnsoji, Shell .spiral, rolled on the same plane; whorls at 



