194 
THE LIAS AMMONITES. 
But the Ammonites of the St. Cassian (Triassic) beds with Ammonites Aon, Munster, 
were not comprehended in a distinct group. 
M. Alcide d'Orbigny divided the Ammonites into twenty-one sections in these he 
inchided the groups estabHshed by von Buch, and added others to receive the many new 
forms which he had discovered among the very rich materials he had assembled for his 
great work on the Terrains Cretacee and Terrains Jurassique of France. 
a. Species ivitli a siphonal keel entire. 
1st Section. Arietes, von Buch. See page 186. 
2nd Section. Falciferi, von Buch. See page 187. 
3rd Section. Cristati, d''Orhigny. Shell compressed, sides ornamented with ribs, 
bifurcated and bent forwards without forming an angle ; with or without prominent tuber- 
cles. Siphonal area prominent in the keel, which contains the siphuncle. Mouth, when 
Fig. 74. — Schloenhachia Roissyana, d'Orb. Fig. 75. — Schloenbachia cristata, Deluc. 
perfect, prolonged into a prominent rostrum upon the median line of the margin. Septa 
formed of lobes, in general divided into unequal parts and into equal saddles. Siphonal 
lobe longer than the superior lateral. The lateral saddle less elevated than the others. The 
siphonal saddle very high. The best types are Schloenbachia cristata, Deluc (fig. 75), 
and Schloenhachia Boissyana, d'Orb. (fig- 74), both from the Cretaceous Formations. 
h. Species with the siphonal area canaliculated. 
4th Section. Tuberculati, d' Orbiyny. The sides of the shell ornamented with ribs 
and tubercles. Siphonal area provided in the middle with a deep well-defined channel. 
Mouth, when complete, representing an elongated rostrum corresponding to the siphonal 
^ ' Paleontologie Fran9aise ; Terrains cretaces,' torn, i, p. 405, 1S40. 
