96 



Shell; equivalve, sometimes thin, sometimes rather solid, often 

 pearly within, covered externally with a brownish, or shining 

 olive, horny epidermis ; umboes contiguous, the ligament being 

 contained in a central internal pit, on either side of which the 

 teeth are numerous and comb-like. 



An interesting and rather extensive series of bivalves, mostly small, are 

 included under this head, comprising two well-marked divisions. In the 

 first, the Nucules proper, the mantle-lobes of the animal are freely open, 

 without siphonal tubes. In the second division, which, further subdivided, 

 form the genera Leda and Yoldia of authors, there is a pair of small si- 

 phonal tubes. The shell is characterized throughout by a row of fine 

 comb-like teeth, and the ligament, instead of being external, is contained 

 within a central internal pit. The substance of the shell is thin, covered 

 mostly by a shining horny epidermis, and the inner surface is generally 

 pearly. 



The Nuculce are deep-dwelling mollusks, inhabitants chiefly of the boreal 

 and arctic seas. 



1. arctica, Gray. 



2. Belcheri, Hinds. 



3. Bellotii, Adams. 



4. bellula, id. 



5. buccata, St imp. 



6. cselata, Hinds. 



7. Cascoensis, Migh. 



8. castanea, Adams. 



9. castrensis, Hinds. 



10. Chuva, Gray. 



11. complanata, Moll. 



12. concinna, Adams. 



13. convexa, Sow. 



14. costellata, id. 



15. crassa, Hinds. 



16. crenifera, Sow. 



17. crispa, Hinds. 



18. Cumingii, id. 



19. cuneata, Soto. 



20. curvirostrata, id. 



21. decens, Adams. 



22. declivis, Hinds. 



23. decora, Adams. 



Species. 



24. decussata, Sow. 



25. delectabilis, Adams. 



26. delphinodonta, High. 



27. divaricata, Hinds. 



28. eburnea, Sow. 



29. electa, Adams. 



30. Elenensis, Sow. 



31. elongata, id. 



32. emarginata, Lam. 



33. excavata, Hinds. 



34. exigua, Sow. 



35. fabula, id. 



36. fastidiosa, Adams. 



37. fulgida, id. 



38. gibba, id. 



39. gibbosa, Sow. 



40. glacialis, Gray. 



41. gloriosa, Adams. 



42. hyperborea, Love'n. 



43. inconspicua, Adams. 



44. inornata, id. 



45. Jamaicensis, D'Orb. 



46. Japonica, Adams. 



47. laevigata, Spengl. 



48. lanceolata, Lam. 



49. lata, Hinds. 



50. Layardii, Adams. 



51. lepida, id. 



52. lepidula, id. 



53. lhnatula, Say. 



54. lucida, Gould. 



55. lucida, Loven. 



56. lugubris, Adams. 



57. lyrata, Hinds. 



58. margaritacea, Ad. 



59. marmorea, Hinds. 



60. micans, Adams. 



61. minuta, Mull. 



62. mirabilis, Adams. 



63. mitralis, Hinds. 



64. Mulleri, Gray. 



65. myalis, Couth. 



66. nana, Hinds. 



67. nasuta, Sow. 



68. navicularis, Couth. 



69. Nicobarica, Za?«. 



