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 G*ray, King, Voy. N. H. 



§§ Shell solid. Umbones close, 



Ligament very oblique, submarginal. Lateral 

 Teeth smooth. 



11. Mactra cygnea ? Chenin. 



Inhabits China. 



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



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



Shell trigonal. 



13. Mactra stridtula 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,ralher long, very close to the cardinal Teeth {the 

 front ones from near the umbo, and furnished ivith a thickened 2)rocess at its 



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



15. Mactra plicatdria 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. Siphonat 'inflection ovate, 



