76 



PALAEONTOLOGY. 



The genus Astarte, now limited to a dozen species in the 

 North Atlantic and Arctic seas, has an almost world-wide 

 geological distribution, and counts 200 species in d'Orbigny's 

 catalogue, commencing with the lias period. Crassatella, now 

 almost a southern form, is common in the cretaceous and 

 tertiary strata of Europe. Closely allied to Astarte is the 



Fig. 20. 

 Secondary and Tertiary Bivalves. 



i. Pachyrisina septiferum, Bur.; Corallian, Meuse. 



2. Cardinia hybrida, Sby. ; Lias, Gloucester. 



3. Opis lunulatus, Mill. ; Inf. Oolite, Bayeux. 



4. Tancredia securiformis, Dkr. ; Lias, Saxony. 



5. Sowerbya crassa, d'Orb. ; Oxfordian, Ardennes. 



6. Goniomya scripta, Sby. ; Kelloway rock, Wilts. 



7. Lithocardium aviculare, Lam. ; Eocene, Paris. 



8. Grateloupia irregularis, Bart. ; Miocene, Bordeaux. 



9. Teredina personata, Lam. ; Eocene, Bognor. 



extinct genus Opis (fig. 20, 3), of which there are 42 species 

 in the secondary series ; and Cardinia (fig. 20, 2), characteristic 

 of the lias and oolites. The so-called Unios of the coal 

 measures (Anthracosia, King) are probably members of this 

 group * One hundred species of Cardita (including Veneri- 



* "They occur in the valuable layers of clay-ironstone called 'mussel- 

 bands,' associated with Nautili, Discinm, etc. In Derbyshire the mussel-band 

 is wrought, like marble, into vases." — Woodward. 



