PLATE XV. 



Fig. 



1. Bysso-arca tumida, /. Soioerhy. Right aspect of a testiferous specimen, natural 



size. Tunstall Hill. Belonging to Professor Phillips. 



2. — — Umbonalaspect (rather enlarged) of a left valve (testiferous), 



showing cartilage-grooves on the area. Tunstall Hill. 



3. — — Umbonal aspect, natural size. Tunstall Hill. 



4. — — Umbonal aspect, natural size. Tunstall Hill. 



(The circular hole in one of the beaks is supposed to have been made 

 by a carnivorous mollusc.) 



5. — — Ventral aspect (natural size) of a testiferous specimen, 



showing byssal opening. Tunstall Hill. 



6. — — Right valve, twice the natural size. Tunstall Hill. 



7. Bysso-arca striata, ScJdotheim. Right valve (a little enlarged) of a testiferous 



specimen. Tunstall Hill. 

 8 — — Cast of the right valve (natural size), showing impressions 



of the anterior and posterior teeth. Humbleton Hill. 



Belonging to Mr. J. de C. Sowerby. 

 9. — — Cast, natural size. Humbleton Hill. 



10. Bysso-arca Kingiana, de Verneuil. Left valve of a testiferous specimen, natural 



size. Tunstall Hill. 



11. — — Right valve (twice the natural size) of a testiferous specimen. 



Tunstall Hill. 



12. — — Umbonal view of the same valve. 



13. Pleurophorus costatus. Brown. Right valve; testiferous, natural size. Tunstall 



Hill. 



14. — — Left valve ; testiferous, natural size. Tunstall Hill. 



15. — • — Cast of a right valve (natural size), showing impressions of 



the anterior and posterior adductor muscles, and 

 pallial ditto. Humbleton Hill. 



16. 17. — — Interior of both valves (twice the natural size), showing 



anterior adductor muscular impression {a) ; ridge on the 



posterior side of the last [b) ; and cartilage fulcrum (c). 



Byers's Quarry. 

 18, 19. — — Interior of both valves (twice the natural size) of a young 



individual ; testiferous. Byers's Quarry. 

 20. — — Right valve (natural size) of a smooth variety; testiferous. 



Byers's Quarry. 



