372 



Certain Shells in the British Museum, 



8. Mactra Chemnitzii Gray. ; M. violacea austr&lis Chemn., f. 1954. 



9. Mactra pulchra Gray. 



10. Mactra abbrevidta Gray, King, Voy. N. H. 



§§ Shell solid. 



Umbqnes close. Ligament very oblique, submarginal. Latei'al 

 Teeth smooth. 



11. Mactra cygnea ? Chemn. 



Inhabits China. 



12. Mactra rufeatens Lam. Hinder lateral teeth rather the shortest. 



B. The kinder lateral Tooth very small, close; the anterior one elongate. 



Shell trigonal. 



13. Mactra striatula Linn.; M. carinata Lam. 



14. Mactra exoleta n. s. Shell trigonal, white, thin, pellucid, slightly con- 

 centrically striated ; covered with a thin pale periostraca ; the anterior 

 slope compressed, produced; the hinder slope ventricose, flattened, edged, 

 with a slightly raised keel. 



Inhabits . 



C. The lateral Teeth subequal, rather long, very close to Hie cardinal Teeth {the 

 front ones from near the umbo, and furnished with a thickened process at its 



tipper part). Shell thin, trigonal. Hinge-margin 2-edged. 



15. Mactra plicataria Chemn. {fig. 

 31.), vi. f. 202. 204., Gmel.; M. 

 subplicata Wood. Supp., t. 1. 

 f.6. 



16. Mactra Reevesii Gray. Shell 

 wedge-shaped, thin, white, pel- 

 lucid, striated ; concentrical 

 curved near the umbo. 



Inhabits China. {J. R. Reeve, 

 Esq.) 



17. Mactra subplicata Lam., not 

 Wood. 



D. The hinder lateral Tooth short, close to the cardinal ones ; the anterior one 

 elongate, compressed, thin, considerably below the Hinge Teeth. Shell thin. 

 Hinge-margin double. 



18. Mactra violacea Chemn., vi. f. 213, 214. ; Ency. Method., t. 254. f. 1. 



Inhabits Tranquebar. 



E. The lateral Teeth very small, short, quite close up to the Hinge Teeth, and 

 scarcely separated from them. Hinge-margin double. Shell very thin; 

 hinder slope keeled. 



19. Mactra elegans Sow. Tank. Cat. f. 



Inhabits Florida. 



20. Mactra vitrea Gray. Shell oblong trigonal, thin, white, pellucid. Um- 

 bones incurved, subposterior. Anterior slope flattened'; edge waved. Lu- 

 nule depressed, lanceolate. Hinder slope compressed. Lozenge elongate, 

 with a slight rib-like raised edge. The cavity in the front of the hinge- 

 margins very long and deep. 



Some affinity to M. recurva and to M. subplicata Lam. 

 Inhabits . British Museum. 



III. Spi'sula Gray. 

 Shell ovate, trigonal, subangular at each end. Hinge and lateral teeth 

 as in Mactra ; but hinge tooth of left valve small. Siphonal inflection ovate, 



