PLATE XVIII. 



Oris (continued). 

 Figs. 



1. Opis haldonensis, Woods. Upper Greensand, Haldon. British Museum, 

 No. L 17143. a, exterior ; b, interior of right valve ; c, posterior view 

 of the same; d, anterior view. (P. 1 ID.) 



Genus — Caedita, Bruguiere. 

 2-4. 0. ? fenestrate). (Forbes). Lower Greensand (Pema-bed), Atherfield. 

 (P. 121.) 



2. Museum of Practical Geology, No. 14360. a, left valve ; b, dorsal view, X H ; 



c, median part of left valve, x 4. 



3. Sedgwick Museum. Eight valve, x 1|. 



4. Sedgwick Museum, a, left valve; b, anterior view. 



5. C. upicarensis, Woods. Lower Greensand, Upware. Sedgwick Museum. 



a, right valve; h, dorsal view; c, anterior view; <1, part near the 

 middle of the right valve, X 4. (P. 122.) 



6. 0. sp. Lower Greensand (Perna-hed), Atherfield. Sedgwick Museum. 



a, left valve ; b, dorsal view ; c, part near the middle of left valve, 

 X 5. (P. 123.) 



7-14. G. tenuicosta (Sow.). Gault, Folkestone. 7-13. Sedgwick Museum. 

 14. British Museum, No. 48135. (P. 124.) 



7. Left valve, x H. 



8 a, left valve ; b, anterior view. 



9. Right valve. 



10 a, left valve ; b, dorsal view ; c, part near the mid-ventral border, x 6. 



11 a, right valve, x 1% ; b, dorsal view, x If ; c, part near the middle of the right 



valve, x 6. 



12. Left valve, x 2. 



13. Inflated variety, a, right valve ; b, dorsal view. 



14. Short and much inflated variety. <i, right valve , b, dorsal view. 



15, Hi. G. Gottaldina, d'Orb. Chloritic Marl. (P. 126.) 



15. Toller Fratrum. Museum of Practical Geology, No. 14348. Right valve. 



16. Chard. Oxford Museum, a, left valve j b, dorsal view. 



17,18. C. cancella ta, "Woods. Chalk Rock, Cuckhamsley. Sedgwick Museum. 

 (P. 127.) 



17 a, wax cast of right valve, x 1\ ; b, ornamentation near the middle of the 



right valve, x 5. 

 18. Natural internal cast. a, left valve; b, anterior view. 



