PLATE XIX. 



Dreissensia (continued). 

 Fios. 



]— 11. D. lanceolafM (i^ow.). (P. 110.) 



1 — 3. Crackers, Atherfield. 



1. Leckenby Collectiou, Woodwardian Museum, a, left valve ; h, ventral — 



showing opening for byssus. 



2. Wiltshire Collection, Woodwardian Museum, a, right valve ; h, ventral. 



3. Leckenby Collection. Right valve. 



4. Perna-hed., Atherfield. Wiltshire Collection, Woodwardian Museum, a, 



left valve ; h, interior of same. 



5. Upper Greensand, Shaftesbury. British Museum, No. 88,894. Left valve. 



6 — IL Greensand, Blackdown. 



6. Wiltshire Collection, Woodwardian Museum, a, left valve ; b, part near 



the umbo x 2 ; c, dorsal of both valves. 



7. Wiltshire Collection, a, right valve; b, ventral; c, interior of same. 



8. Bristol Museum. The type of Mytilns prselongus, Sowerby. 



9. 10. Wiltshire Collection. Left valves. 



11. Bristol Museum. One of the types of Mytihis tridens, Sowerby. a, right 

 valve ; b, antero-ventral. 



Genus — Tkiconia, Brnguiere. 



12. T. dnnscombensiti. Lye. Cenomanian (Bed 11), Humble Point, Lyme 



Regis. Museum of Practical Geology (No. 6774). a, right valve; 

 h, dorsal. (P. 78.) 



13. T. oriiata, d'Orb. Hytlie Beds, Lympne. Museum of Practical Geology 



(No. 6771). Left valve. (P. 85.) 



14. '/'. crenulata, Lam. Cenomanian (Bed 10), Dunscombe. Mr. Meyer's 



Collection. Left valve. (P. 82.) 



