Fig. 



17. Productus aculeatus. Another similar example, but with a longer hinge- 



line. Limestone, Settle. 



18. ,, „ var. P. laxisjrina, Phillips. Prom the figure in the 



1 Geology of Yorkshire.' 



19. ,, ,, A large, older, and more spiny example, from Chrome 



Hill, Longnor, Derbyshire. Museum of Practical 

 Geology. 



20. „ „ P. spinuloses, Phillips (not Sow.) From the figure in the 



' Geology of Yorkshire' (pi. vii, fig. 14). 



21. ,, Youngianus, Dav. From the Carboniferous limestone of Corrie- 



burn, Stirlingshire, and collection of Mr. 

 J. Young. 



22. „ „ From Bolland. 



23. „ „ From Settle, Yorkshire. 



24. „ tessellatus, Be Koninck. From the Carboniferous limestone, Isle 



of Man, nat. size. 



25. „ „ A specimen deprived of its fringes, from Settle, in 



Yorkshire, 



