196 THE LIAS AMMONITES. 



the siplional area compressed tubercles, which collectively represent a series of crests. 

 Septa formed of lobes divided into single parts, and of saddles divided into pairs of parts. 

 Siphonal lobe nearly equal in length to the inferior lateral lobe. Eoplites Brottianus, 

 d'Orb. (fig. 78), from the Lower Cretaceous Rocks, is a good type of this section. 



8th Section. Rhotomagenses, d'Orhi^ny. Shell with inflated whorls, square or 

 oval, ornamented with prominent ribs, more or less tuberculated upon four or five lines, 

 one of which runs along the median line of the area, and renders it more or less 

 angular. Septa formed of lobes and saddles partly divided into pairs. The siphonal 

 lobe longer than the superior lateral. The species characterise the Middle Cretaceous 

 Pormation, and Hoplites Deverianus, d'Orb. (fig. 79), from the Upper Greensand, is a 

 good type of this section. 



e. Species with the siphonal area excavated, and provided with tubercles on the sides. 

 9th Section. Dentati, von Buch. See p. 192. 

 10th Section. Ornati, von Buch. See p. 19:2. 



/. Species with the siphonal area more or less square. 

 11th Section. Elextjosi, von Buch. See p. 193. 



12th Section. Compressi, d'Orhigny. >S'M/ in general very 

 much compressed, composed of large whorls, highly involute. 

 Sides provided with radii or fine striae, all slightly flexed, and 

 passing on to the margin of the siphonal area, where they develop 

 small tubercles. Siphonal area narrow and squarely truncated. 

 Sej)ta composed of a great number of lobes formed of single parts, 

 and of saddles often formed of pairs of parts, Siphonal lobe very 

 large, much longer than the superior lateral. These Ammonites all 

 appertain to the diflerent divisions of the Cretaceous Formation, 

 Cos. Beaumoniianum, d'Orb. Cos. Beaumontianum, d'Orb. (fig. 80), from the Lower Chalk, is a 

 good type. 



13th Section. Armati, von Buch. See p. 191. 



14th Section. Angulicostati, d' Orhigny. Shell thick, with whorls almost round, each 

 side of the siphonal area ornamented throughout with slight ribs which make this part 



I 



