LAMELLIBRANCHIATA. 



50 recent forms, one only is Arctic, and this occurs in the 

 glacial deposits of England. The allied genus Myoconcka 

 is characteristic of the older secondary rocks, and Hippo- 

 podium of the lias. 



Fig. 16. 

 Secondary and Tertiary Bivalves. 



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



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



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



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



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



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



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



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



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



The Veneridcs are pre-eminently characteristic of the tertiary 

 and present period. Some obscure species of Venus are found 

 in the oolites : Gytherea occur in the greensands ; Artemis, 

 Triijona, Lucinopsis, Venerupis, and Tapes appear in the middle 

 tertiary ; Petricola in the eocene. The only extinct form is 

 Grateloupia (fig. 16, 8), which differs but little from Trigona. 



The Mactras and Tellens are also comparatively modern 

 groups ; most of the supposed oolitic species belong to Luci- 

 nidce, except Sowerbya (fig. 16, 5), which has a pallial sinus, 

 and is found in the oolites of Malton and Portland. Psam- 



