PLATE XIT. 



Fig. 



19. Strophalosia Morrisiana, King. Enlarged view of the posterior part of the last 



specimen, showing the area of the large valve (a), with 

 its deltidium (3), and the area of the small valve (c). 

 (Letter a should have pointed to the upper area). 



20. — — Cast, natural size, large valve. Humbleton Hill. 



21. — — Ideal medio-longitudinal section of the last specimenj 



showing it to be tri-valved : a, large valve ; b, small 

 valve ; c, inner valve. 



22. — — Same specimen as fig. 20, exhibiting impression of the 



inner surface of the small valve (3). 



23. — — Same specimen, with the part (5) of the last figure removed, 



thereby disclosing the impression of the inner valve (c). 



24. — — Another tri-valved specimen. Cast, natural size : a, 



inner surface of large valve ; c, inner valve ; d, im- 

 pression of the outer surface of the small valve. 

 Humbleton Hill. 



25. — — Cast, large valve, natural size. Humbleton Hill. 



26. — — Gutta-percha cast of the outer surface of the small valve, 



showing the spines. Original from Whitley. 



27. — — Large valve of a young specimen, magnified four times. 



Tynemouth Cliff. 



28. — — Small valve of last specimen, showing bases of spines. 



29. — — Large valve, natural size, with portions of the test remaining 



where the spines are preserved. Humbleton Hill. 



30. — — Cast, natural size, ventral valve. Humbleton Hill. 



31. — — Gutta-percha cast (natural size) of small valve with the 



hinge-plate of the large valve attached to it : a, teeth 

 of the large valve inserted in the sockets (which are 

 not so clearly exhibited as could be desired) on each 

 side of the median plate of the small valve. Original 

 from Humbleton Hill. 



32. — — Cast, natural size, small valve. Humbleton Hill. 



33. Strophalosia parva, King. Cast (rather larger than the original) adhering by 



its spines to the inner surface of the large valve of 



a Productus horridus. Humbleton Hill. 



(The outline of the Productus is not represented on account of the 



want of space. The letter a points to the umbone of the 



Strophalosia). 



