138 



Genus 2. AMPHIDESMA, Lamarck. 



Animal ; undescribed. 



Shell ; equivalve, inequilateral, oblong-oval or rounded, posterior 

 side generally more or less flexuous ; hinge composed of one or 

 two teeth in each valve, with an obliquely elongated pit lying 

 betioeen them containing the ligament ; there is also a thin ex- 

 ternal ligament. 



The genus Amphidesma shows rather a want of scientific spirit among 

 naturalists residing and collecting abroad. Had any one of the sixty beau- 

 tiful species at present known been a native of the shores of Europe or of 

 North America, its animal would have been described long ago ; but half 

 a century, nearly, lias elapsed since Lamarck drew attention to the pecu- 

 liarities of the shell of Amphidesma, and abundance of specimens, of bold 

 dimensions and attractive colouring, have been brought from the western 

 coast of South and Central America, from Australia, from the Philippine 

 Islands, yet no one has preserved the animal, and authors are altogether 

 silent on the matter. 



Amphidesma has a particularly characteristic hinge. It has two liga- 

 ments, one internal, solid, and conspicuous, contained within a pit running 

 obliquely on the posterior side ; the other thin and external. The shell is 

 mostly of an oblong-circular or oval form, with the posterior or hinge side 

 more or less truncated and flexuous. The sculpture consists chiefly of 

 irregular conceutric ridges, often in densely packed lamellae, neatly frilled, 

 with the interstices profusely cancellated. The species have all a light 

 and delicate aspect, though in several instances they are rather solid ; some 

 are white, some are painted with rose and pale yellow. 



, 1. amabilis, Adams. 



2. amoena, id. 



3. australis, Sow. 



4. bicolov, C. B. Adams. 



5. Calif ornica, Adams. 



6. cancellata, Sow. 



7. cornicolor, Hani. 

 3. casta, Adams. 



9. compta, id. 



10. cordiformis, Chemn. 



11. corrugata, Sow. 



Species. 



12. crenulata, id. 



13. crocea, Gould. 

 1-i. decisa, Conr. 



15. decora, Adams. 



16. decussata, Wood. 



17. deformis, Phil. 



18. duplicata, Sow. 



19. elliptica, id. 



20. exarata, Ad. ^' Reeve. 



21. formosa, Sow. 



22. Gruneri, Adams. 



23. icterica, Reeve. 



24. Jovis, Adams. 



25. jucunda, id. 



26. Jukesii, id. 



27. lseta, id. 



28. lsevis, Soto. 



29. lamellosa, id. 



30. lenticularis, id. 



31. luteola, id. 



32. Martinii, id. 



33. modesta, id. 



