FOSSIL FAUNA. 145 



PLATE LXIII. 



TrIGONIjE. 



Figs. 1, & 2, represent the structure of the hinge in both valves of a genus of bivalves of 

 which numerous fossil species are met with in the secondary strata, and two or three 

 species still exist in the Pacific Ocean. The genus is named Trigonia, from the form 

 of the hinge, and the specific names below are those given by Mr, Parkinson. 



Fig. 3. Trigonia clavellata, of Parkinson, from the Kimmeridge clay, Hartwell, Bucks. 



Fig. 4. Trigonia costata, Oxford clay, Wilts. 



Fig. 5. Trigonia excentrica; upper greensand, Blackdown. Like most of the shells from this 

 locality, the Trigonia are transmuted into silex. 



Fig. 6. Trigonia dwdalea, Blackdown. 



Fig. 7. spinosa, Blackdown. 



Fig. 8. Enlarged view of the spines of the above. 



Fig. 9. Trigonia alceformis, Blackdown. 



Fig. 10. rudis, Blackdown. 



Fig. II. a bivalve shell of the genus Productus [P. antiqiiatus, of Sowerby?), from the Moun- 

 tain limestone. See description of fig. 9, Plate LXVII. 



Fig. 12. Cast of a species of Trigonia {T. clavellata), from the Portland rock. Many beds of 

 this oolitic limestone are almost entirely made up of casts of Trigonise, and chiefly of 

 this species. 



Fig. 13. Trigonia sinuata, from Blackdown. 



Figs. 14 to 18. "Different views of a species of Harpaa-." — Mr. Parkinson {Plicatula spinosa). 

 From the Lias, Gloucestershire. 



Fig. 14. The inner surface of the flat valve. 



Fig. 15. Inner surface of the convex valve. 



Fig. 16. Magnified hinge teeth of the flat, and fig. 17, of the convex valve. 



Fig. 18. Magnified view of the adpressed spines on the external surface of the shell. 



