PLATE XIII. 



Fig. 



1. Pecten pusillus, Munster. Cast of upper valve, natural size. Humbleton Hill. 



2. — — Cast of under valve, natural size. Humbleton Hill. 



(The radiating longitudinal lines on the fossil figured, are due to a con- 

 dition of fossilization.) 



3. — — Lateral view of a cast, natural size. Humbleton Hill 



4. Lima Permiana, King. Left valve (testiferous), natural size. Humbleton Hill. 



5. Monotis speluncaria, ScJdotheim. Cast of UDper valve, natural size. Humbleton 



Hill. 



6. — — Cast of upper valve, natural size. Humbleton HiU. 



7. — — Cast of the last specimen, showing byssal notch {a). 



8. — — Cast of upper valve, natural size. Humbleton Hill. 



9. — — Cast of upper valve, natural size. Humbleton Hill. 



10. — — Under valve of last. 



11. — — Upper valve of a smooth (testiferous) variety, natural size. 



Tunstall Hill. 



12. — — Upper valve of a dextrally-oblique variety. Cast, natural 



size. Humbleton Hill. 



13. — — Upper valve (testiferous) of a sinistrally-oblique variety, 



natural size. Tunstall Hill. 



14. — • — Outer surface of a flat valve (testiferous), showing radiating 



longitudinal lines ; enlarged. Tunstall Hill. 



15. — — Upper valve of a young testiferous specimen. Twice the 



natural size. Tunstall Hill. 



16. — — Under valve of the same shell. 



17. — — Cast of upper valve, natural size. Humbleton Hill. 



18. — — Lateral view of specimen at figs. 9, 10. 



19. — — Umbonal view of the same. 



20. — — Cast of under valve (natural size) showing impressions of 



the adductor muscle {a), pallial line {b), and pedal 

 muscles (c). Humbleton Hill. 



21. — — Testiferous specimen. Upper valve, natural size. Silks- 



worth. 



22. Monotis radialis, Phillips. Cast of upper valve, natural size. Humbleton Hill. 



23. — — Cast (natural size) of the upper valve of a smooth variety. 



Humbleton Hill. 



(The margia of the original is not entire.) 



24. Monotis Garforthensis, Kinc/. Testiferous specimen. Upper valve, natural size. 



Garforth. 



(The specimen is in the Museum of the Yorkshire Philosophical 



Society.) 



25. Monotis ? Testiferous specimen exhibiting the inner surface of 



the under valve, natural size. Garforth. Mr. E. 

 Charlesworth's specimen. 



