410 STRATIGRAPHICAL GEOLOGY 



Zone. 



fClydoniceras discus. 

 Bath Oolites | Waldheimia digona. 



or Bathonian "I Oppeliafusca and Macrocephalites subcontracts. 

 \Parkinsonia Parkinsoni. 



Cceloceras Blagdeni. 



Inferior Oolite I Witchdlia Ammonites. 

 orBajocian \Lceras concamim. 



Ludivigia Murcntsonce. 

 Lioceras opalinum. 



B. LIFE OF THE PERIOD 



Marine Fauna. The fauna of the Middle Jurassic rocks is 

 closely related generically to that of the Lias, but differs princi- 

 pally in the relative abundance of Corals, Echinoderms, and Gastro- 

 pods. This, however, is sufficiently explained by the fact that 

 these limestones were evidently formed in clear water, and some- 

 times in the neighbourhood of coral reefs. Brachiopoda, too, are 

 individually very abundant, though the number of species is not 

 greater than in the Lias, and the genera are the same, except that 

 Cadomella and Spinferina, are absent. The following are the more 

 important genera which now appear, and those to which an 

 asterisk is prefixed did not survive the Jurassic period : 



Porifera. Corynella, Craticularia, Holcospongia, Lymnorella, 



Peronidella, Verrucocselia. 

 Anthozoa. Phyllocaenia ( = Adelastrea), *Anabacia, Cryptocoenia, 



Cyathophora, Stylina. 

 Echinoderma. Apiocrinus, *Clypeus, Collyrites, Nucleolites, Hemici- 



daris, Holectypus, *Hyboclypeus, Pedina, Pygaster, 



Pygurus, Stomechinus. 

 Brachiopoda. Terebratulina. 

 Lamellibranchia. Corbis, Corbicella, Cyprina, Isocardia, *Pachyrisma, 



Pteroperna, Sowerbya, Spondylus, *Trichites. 

 Gastropoda. Brachytrerna, Bulla, *Cirrus, Dephinula, Fissurella, 



Nerineea, Pileolus, *Purpuroidea, Rissoina. 

 Cephalopoda. The Ammonite genera Cosmoceras, *Haploceras, 



Lioceras, Ludwigia, Macrocephalites, Oppelia, 



*Parkinsonia, Perisphinctes, Sonninia, and Sphsero- 



ceras. 

 Pisces. Aspidorhynchus, Microdon, Strophodus, Ganodus, 



Ischyodus. 

 Reptilia. Streptospondylus, Teleosaurus. 



The following are lists of the fossils which may be regarded as 

 specially characteristic of the groups indicated : 



Fossils of the Bajocian (Inferior Oolite} 



Actinozoa. Anabacia hemispherica, Thecosmilia gregaria. 



Echinoderma. Stomechinus germinans, Pygaster semisulcatus, Hybo- 

 \ clypeus agariciformis. 



