54 CONCU\L\k—DITUYRA. 17. 



Mactra alba. Linn. Trans, vi. tab. 18, %. 9 to 12. 



Mus. nost. ^ English and Irish coasts. 



Shell more than half an inch long, and three quarters broad, 

 thin flat, glossy white, a little angular at one of the sides when 

 full grown : beaks not quite central : inside smooth glossy 

 white. 



pui|«)rea. 

 1. 



17. AGl^A—TURTON. 



Testa, tranversa, ovata, teqiiivalvis, ina;quilateralis, latere 

 antico hiante. Cardo dente nnico erecto conico penetranie 

 in utrdque valvd: lateralibus niiUis. Ligamenttim exter- 

 num. 



Shell transverse, oval, equivalve, inequilateral, open at the an- 

 terior end. Hinge with a single erect conic penetrating tootli 

 in each valve : lateral teeth none. Ligament external. 



Agina. 



Tab. nost. 4, fig. 9. 

 Mya purpurea. Montagu. Test. Brit. Suppl. p. 21. 

 Mus. nost. From rocks in Torbay. 



