PLATE XVIII. 



Oenus — Septifee, lUcluz. 

 Figs. 

 1-12. S. Uneatus {Ho^y.). (P. 106.) 



1. Hythe Beds, Lympne. Museum of Practical Geology, No. 6595. a, left valve ; 



h, dorsal. 



2. Same locality, &c., No. 6595. a, right ; h, autero-veutral. 



3. Hythe Beds, Hythe. Museum of the Geological Society. Eight valve. 



4. Hythe Beds, Lympne. Museum of Practical Geology, No. 6595. a, left valve ; 



h, antero-ventral. 



5. Chalk Marl, Chardstock. Museiim of Practical Geology, No. 6596. a, left valve ; 



h, antero-ventral outline. 



6. Ccnomauian (Bed 12), Kempstone Eocks (Sidmouth). Museum of Practical 



Geology, No. 6773. a, antero-ventral outline; b, right valve x 1|; c, orna- 

 mentation near the centre of the valve x 12 ; f7, ornamentation near the posterior 

 margin X 12. 



7. Cenoraanian (Bed 12), Axmouth. Mr. Meyer's Collection. Antero-ventral of 



left valve. 



8. Cenomanian (Bed 12), Dunscombe. Mr. Meyer's Collection. Left valve. 



9. Chalk Eock (Beussiamnn zone), Cuckhamsley. Montagu Smith Collection, Wood- 



wardian Museum. Eight valve. For figures of a larger example from this zone 

 see 'Quart. Journ. Geol. Soc.,' vol. liii, 1897, pi. xxvii, figs. 11, 12. 



10. Chalk Eock, Dullingham. Woodwardiau Museum. Internal mould, a, right 



valve ; b, antero-ventral. 



11. Chalk Eock, Winchester. Mr. E. M. Brydoue's Collection, a, left valve; 6, antero- 



ventral. (Figured 'Quart. Journ. Geol. Soc.,' vol. liii, 1897, pi. xxvii, figs. 9, 10.) 



12. Flint gravel (derived from Upper Chalk), near Ventnor. Left valve, somewhat 



flattened by crushing. 



Genus — Dreissensia, van Beneden. 



13 — 15. D. lanceolata (Sow.). Crackers, Atherfiekl. (P. 110.) 



13. Left valve. Wiltshire Collection. 



14. Left valve. Woodwardian Museum. 



15. Eight valve. Woodwardian Museum. 



