PLATE VIII. 



Fig. 



11. Trigonotreta cristata, xSfc^/o^i^em. Cast showing area and fissure, natural size. 



Humbleton Hill. 



12. — — Young specimen. Humbleton Hill. 



13. — — Enlarged view ofthe test, showing openings of the punctures. 



14. — — Longitudinal section of the test, highly magnified, showing 



casts of the punctures. 



1 5. Trigonotreta multiplicata, /. de C. Sowerhy. Testiferous specimen, a little enlarged, 



of large valve. Tunstall Hill. 



16. — — Small valve of last specimen. 



17. — — View of the area and fissure of the last. 



18. — — Interior of the large valve, showing the ventral median 



plate {a). Tunstall Hill. 



19. Trigonotreta Jonesiana, King. Large valve of a young specimen, twice the natural 



size. Ryhope Field-House Farm. 



