PLATE XL 



1 . Productus horridus, /. de C. Sow. Testiferous specimen, natural size. Whitley. 



2. — — Testiferous specimen, natural size. Derbyshire. Mr. J. de C. 



Sowerby's specimen — the original of fig. 1 in plate 

 cccxix of the ' Mineral Conchology.' 



3. — — Large valve of another testiferous specimen from Derby- 



shire. Mr. J. de C. Sowerby. 



4. — — View of a specimen partially deprived of the shell, natural 



size. Humbleton Hill. 



5. — — Right half of a testiferous specimen, natural size, showing 



the cardinal spines of both valves. Humbleton Hill. 



6. ■ — — - Impression of the left half of the small valve, natural size, 



showing the pits of a single row of cardinal spines. 

 Humbleton Hill. 



7. — — Impression of the external surface of the small valves, 



showing abortive spmes. Humbleton Hill. 



8. — — Large valve, a little enlarged, of a young (testiferous) 



specimen. Tynemouth Cliff. 



9. — — Small valve of the last specimen, showing bases of the 



spines. 



10. — — Gutta-percha cast of the small valve (inner surface), showing 



the boss or cardinal muscular fulcrum {a); median 

 plate {b) ; posterior division of the vahoilar muscular im- 

 pressions (c) ; anterior division of ditto {dy ; (?) impres- 

 sions of the inferior pedicle muscles (e) ; reniform im- 

 pressions (/). The original is from Humbleton Hill. 



11. — — Gutta-percha cast of the cardinal boss of a specimen from 



Humbleton Hill. Twice the natural size. 



12. — — Cardinal boss of a specimen from Garmundsway. 



(The upper part of the figure is foreign matter.) 



13. — — Magnified representation of the structure of the shell : a, ex- 



ternal surface of the shell, exhibiting lines of growth : 

 b represents the external layer removed, thereby ex- 

 posing the under fibrous layer. Mr. J. de C. Sowerby's 

 specimen, from Derbyshire. 



14. Productus umbonillatus, Kinff. Convex valve, natural size, with a portion of the 



shell, showing bases of spines. Tunstall Hill. 



