167 

 M. A. d'ORBiGNY grouped Ammonites into 21 sections, founded upon 

 the classification of vonBuch, these are, 



(A.) — Species with an entire dorsal keel 



SECTION EXAMPLE DISTRIBUTION 



1 Arietes, von Buch A. BucUandi, Sow. Lower Lias 



2 Falciferi, von Buch A. serpentinus, Schloth. Upper Lias 



3 CaiSTATi, d'Orb. A. cristatus, Deluc. Cretax;eous 



^B.) — Species with the back charvmlled 



4 Ttjbercxjlati, d'Orb. A. awritus,^o^. Cretaceous middle 



(Q.)Species with the hack sharp without being in a keel. 

 6 Clypeiformi, d'Orb. A. GoupiHantis, d'Orb. Cretaceous 



(p.)Species with the back prominent and crenvlaied on the 

 median line. 



6 Amalthei, von Buch A. cordxitus, Sow. Lias and Oolites 



7 Pulchelli, d'Orb. A. Brottianm, d'Orb. Lower Cretaceous 



8 Rhotomagensis, d'Orb. A. Beverianus, d'Orb. Middle Cretaceoiia 



(E.)— /Species ivith the back excavated, provided with tubercles 

 on the sides. 

 9 Dektati, vonBuch A. mamilla/ris, Schloth. Lower Cretaceous 



10 Ornati, 'von Buch A. Duncani, Sow. Middle OoUtes 



rp.) Species with the back more or less squa/re. 



11 Flexuosi, von Buch A. radiatus, Brug. Neocomian 



12 COMPRESSI, d'Orb. A. BeaurmntianusA' Ovh. Cretaceous 



13 Armati, von Buch A. perwrmatus, Sow. Mid &Up. OoUtes 



14 Anguhcostati, d'Orb. A. Martinii, d'Orb. Lower Cretaceous 



15 Capricorni, von Buch A. Capricomus, Schloth. Lias and Oolites 



/(J.) — Species with the back convex. 



16 Heterophylu, d'Orb. A. heterophyllus, Sow. Lias 



17 LiGATi, d'Orb. A. ligatus, d'Orb. Cretaceous 



18 Planolati, von Buch A. communis, Sow. Upper Lias 



19 CoRONARii, von Buch A. Blagdeni, Sow. Inferior OoUte 



20 Macrocephali, v.Buch A. coronatus, d'Orb. Neocomian and 



Oolites 



21 Fimbriati, d'Orb. A. Jimbriatus, Sow. Ditto 



