STRATIGRAPHICAL PAL/EONTOLOGY 403 



CEPHALOPODA : Ammonoidea with ceratitic suture- 

 lines are very abundant, but there are others with more 

 complex (ammonitic) suture-lines. 



Primitive BELEMNOIDEA also occur. 



VERTEBRATA : Reptiles, especially terrestrial forms, 

 are abundant. Some marine reptiles. 



ZONE-FOSSILS : Ammonoids (and Lamellibranchs). 



8. JURASSIC. Echinoids are abundant, especially 

 in certain beds. Clypeus is confined to this system, 

 Hemicidaris nearly so. Acrosalenia, Holectypus, Pygaster, 

 Nucleolites, and Collyrites are Cretaceous also. 



The last spire-bearing Brachiopods occur in the Lower 

 Jurassic. 



Lamellibranchs are abundant, especially Trigonia 

 and Oysters. 



Ammonoidea with highly complex suture - lines 

 (Ammonites) and typical Belemnites are abundant. 



Large marine and terrestrial Reptiles are common. 



LAND-PLANTS {CvcADS, etc.) are common in estuarine 

 deposits. 



The Lower Jurassic is characterized by the presence 

 of the brachiopod Spiriferina, the absence of Irregular 

 Echinoids, and the dominance of keeled forms among 

 the Ammonites (though in particular zones this dominance 

 may be reversed). The Upper Jurassic is characterized 

 by the absence of Spiriferina, the presence of Irregular 

 Echinoids, the dominance of unkeeled Ammonites 

 (reversed in particular zones), and the frequency of 

 lappets on the apertural margin of Ammonites (whether 

 keeled or unkeeled). 



ZONE-FOSSILS. Ammonites or, in their absence, 

 Brachiopods (pp. 385-9). 



9. CRETACEOUS. Echinoids of several new 

 families appear," among which the Echinocorythida. and 

 Spatangidce at once become abundant. 



In the Alpine-Mediterranean province, numerous very 

 peculiarly-shaped inequivalve Lamellibranchs (Rudistes : 

 Monopleura, Caprotina, etc.) occur in the Lower Cretaceous, 

 and are followed in the Upper by the Hippurites, whose 

 habit of growth is more like that of rugose Corals than 

 Lamellibranchs. 



