PLATE XIII. 
Fig. 
. Pecten pusillus, J/inster. 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, Aivg. Left valve (testiferous), natural size. Humbleton Hill. 
5. Monotis speluncaria, Schlotheim. Cast of upper valve, natural size. Humbleton 
Hill. 
— 
6 — = Cast of upper valve, natural size. Humbleton Hill. 
ie — = Cast of the last specimen, showing byssal notch (@). 
8. — = Cast of upper valve, natural size. Humbleton Hill. 
9 — = Cast of upper valve, natural size. Humbleton Hill. 
0 an aa Under valve of last. 
1 
ule — aa 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. 
ihe — soe Cast of upper valve, natural size. Humbleton Hill. 
18. — aaa 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 (4), and pedal 
muscles (c). Humbleton Hill. 
2 a= == 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 margin of the original is not entire.) 
24. Monotis Garforthensis, King. Testiferous specimen. Upper valve, natural size. 
Garforth. 
(The specimen is in the Museum of the Yorkshire Philosophical 
Society.) 
25. Monotis . . . . . 2? Testiferous specimen exhibiting the imner surface of 
the under valve, natural size. Garforth. Mr. E. 
Charlesworth’s specimen. 
