86 



PALEONTOLOGY 



most frequently concealed to some extent, and often marked 

 by cross furrows or " periodic mouths." 



The Ceratites are distinguished by having the lobes of the 

 sutures serrated, while the intervening " saddles" (or curves 

 directed towards the aperture) are simple. They are found 

 in the trias of Europe, Thibet, and South America ; and again, 

 though rarely, in the cretaceous strata of France and Syria — a 

 circumstance quite anomalous in the history of the geological 



Fig. 21. 



i. Ceratites nodosus ; Muschelkalk, Bavaria. 



2. Ammonites Duncani (spinosus, Sby.) ; Oxford Clay, Wilts. 



3. Turrilites. 5. Hamites. 



4. Baculites. 6. Ancyloceras. 



7. (Trigonellites or Aptychus), operculum of Ammonites. 



8. (Rhyncholites hirundo), upper mandible of Nautilus arietis, Rein. Mus- 



chelkalk. 



9. Lower mandible (Conchorynchus avirostris). 



distribution of life. Many Ammonites, perhaps all, are like 

 Ceratites when young. 



A bisected specimen of the Ammonites obtusus, in the 

 Hunterian collection (No. 188), shows well the extent of the 

 last, or inhabited, chamber of the shell, and the effects of the 

 influence of the animal matter of the decaying eephalopod 



