43 Dr. J. E. Gray on some Families of Bivalve Shells. 



5. Harvella. Mactra E., Gray, I. c. Shell cordate, thin, 

 hinder slope keeled, narrow ; hinge-margin double; lateral teeth 

 very small, close up to the cardinal. H. elegans. 



c. Ligament submarginal, triangular, near the cartilage-pit. 



yyi^Y 6- Sjjisula. Shell trigonal, hinder slope more or less keeled ; 



— ' , lateral teeth elongate, cross-ribbed. S. solida. 



d. Ligament internal, in the same closed pit as the cartilage. 



7. Mulinia, Gray, Mag. N. H. i. 372. f. 33 ; P. Z. S. 1847, 

 n. 568. Shell triangular ; lateral teeth short, simple. M. typica. 



8. Gnathodon, Gray, Mag. N. H.i. 373. f. 34; P. Z. S. 1847, 

 n. 569. Shell ovate, triangular, thick, rather produced behind ; 

 lateral teeth elongate, front dilated and angular above. G. cuneata. 



B. Shell oblong or elongate, gaping behind; lateral teeth very 

 small, rudimentary, often obsolete, especially in adult shell; 

 mantle lobes {generally ?) united. Lutrariana. 



a. Ligament external, marginal, separated from the cartilage-pit by 



a shelly plate. 



9. Tresus. Lutraria sp., Middend. Shell ovate oblong, ven- 

 tricose, hinder gape roundish ; cardinal teeth small ; lateral teeth 

 very small, close to the cardinal ; siphonal inflection large, oblong. 

 T. maximus. 



10. Darina. Erycina sp.. King. Shell oblong, compressed, 

 rounded, and slightly gaping at each end; umbo subposterior ; 

 cartilage-pit large ; lateral teeth very small, close to cardinal. 

 D. solenoides. 



b. Ligament subexternal, marginal, not separated from the carti- 



lage. '] 



11. Standella, n. g. Spisula A., Gray, Mag. N. H. i. ]^7i. 

 Shell ovate, hinder slope more or less keeled ; lateral teeth short, 

 smooth, anterior oblique. 



* Oblong, smooth. S.fragilis. ** Oblong, radiately ribbed. 

 S. agyptiaca. 



12. Eastonia. Lutraria C, Gray, Mag. N. H. i. 174. Shell 

 oblong, rather ventricose, thick, equilateral, radiately ribbed, 

 hinder slope rugose, hinder gape small ; cardinal teeth of left 

 valve compressed, nicked ; anterior lateral tooth nearly perpen- 

 dicular. E. rugosa. 



13. Lutraria, Lamk., Gray, P. Z. S. 1847, n. 566. Shell ob- 

 long, elongate, rather compressed, subequilateral ; umbo suban- 

 terior ; hinder gape moderate or large ; cardinal teeth distinct ; 



