Fig 
] 
2. 
10. 
11. 
12: 
PLATE XI. 
; Productus horridus, J. de C. Sow. Testiferous specimen, natural size. Whitley. 
Testiferous specimen, natural size. Derbyshire. Mr. J. de C. 
~Sowerby’s specimen—the original of fig. 1 in plate 
cccxix of the ‘ Mineral Conchology.’ 
Large valve of another testiferous specimen from Derby- 
shire. Mr. J. de C. Sowerby. 
View of a specimen partially deprived of the shell, natural 
size. Humbleton Hill. 
Right half of a testiferous specimen, natural size, showing 
the cardinal spines of both valves. Humbleton Hill. 
Impression of the left half of the small valve, natural size, 
showing the pits of a single row of cardinal spines. 
Humbleton Hill. 
Impression of the external surface of the small valves, 
showing abortive spines. Humbleton Hill. 
Large valve, a little enlarged, of a young (testiferous) 
specimen. Tynemouth Cliff. | 
Small valve of the last specimen, showing bases of the 
spines. 
Gutta-percha cast of the small valve (inner surface), showing 
the boss or cardinal muscular fulcrum (a); median 
plate (4); posterior division of the valvular muscular im- 
pressions (¢) ; anterior division of ditto (7) ; (?) impres- 
sions of the inferior pedicle muscles (e); reniform im- 
pressions (/). The original is from Humbleton Hill. 
Gutta-percha cast of the cardinal boss of a specimen from 
Humbleton Hill. Twice the natural size. 
Cardinal boss of a specimen from Garmundsway. 
(The upper part of the figure is foreign matter.) 
Magnified representation of the structure of the shell: a, ex- 
ternal surface of the shell, exhibiting lines of growth : 
6 represents the external layer removed, thereby ex- 
posing the under fibrous layer. Mr. J. de C. Sowerby’s 
specimen, from Derbyshire. 
14. Productus umbonillatus, Aimy. Convex valve, natural size, with a portion of the 
shell, showing bases of spines. Tunstall Hill. 
