CEPHALOPODA. 



103 



though rarely, in the cretaceous strata of France and Syria 

 — a circumstance quite anomalous in the history of the geo- 

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

 like Ceratites when young. 



A bisected specimen of the Ammonites obtusus, in the 

 Hunterian collection (No. 1 88 Fossil series, Mus. Coll. Chir.), 

 shews well the extent of the last, or inhabited chamber of the 



II ■¥ 



Fig. 31. 



i . Ceratites nodosus Brug. ; Muschelkalk, Bavaria. 



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



3. Turrilites mantelli, Sharpe ; L. Chalk, Lewes. 



4. Baculites anceps, Lam. ; Chalk, Normandy. 



5. Hamites attenuatus, Sby.; Gault, Folkestone. 



6. Scaphites Joanii, Puzos; Nescomian, France. 



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



8. (Bhyncholites hirundo), upper mandible of Xautilus arietis, Rein 



chelhalk. 



9. Lower mandible (Conchorynchus avirostris). 



Mus- 



shell, and the effects of the influence of the animal matter of 

 the decaying cephalopod upon the petrifactive processes after 

 death. The liassic clay has penetrated as far as the retracted 

 soft parts of the ammonite permitted ; the decomposing mollusk 

 had been partially replaced by crystals of calc spar, discoloured 

 by the pigmental or carbonized parts of the animal. The 



