72 



from Mi/tilus, yet there are differences in both the animal and shell which 

 claim attention. The animal of Modiola, so far as it has been examined, 

 has the mantle lobes closed in front, with puckered or pouting orifices, 

 like rudimentary siphons leading to the branchiae. This peculiarity, how- 

 ever, though not in Mytilus proper, exists in the Dreissena section of that 

 genus. The shell of Modiola presents the most obvious difference, being 

 oblong-ventricose and round-shouldered, as it were, instead of elongately 

 fan-shaped, and it is of lighter substance. The animal has, also, the faculty 

 of constructing a sort of entangling nest for itself out of its byssus-ma- 

 terial, w"hich has not been observed in Mi/tilus. 



The Modiola are more numerous in species than the preceding genus, 

 and are equally widely distributed. The genera Crcndla and Modiolarca 

 express the best-marked subdivisions. 



1. albicosta, Lam. 



2. arata, Dunk. 



3. arcuatula, Hard. 



4. arborescens, Chemn. 



5. Australis, Gray. 



6. bavbata, Lam. 



7. Brasiliensis, Chemn. 



8. bulla, Dunk. 



9. capax, Conrad. 



10. cicercnla, Moller. 



11. costulata, Risso. 



12. Cuiningiana, Dunk. 



13. discors, Linn. 



14. elegans, Gray. 



15. elongata, Swain. 



16. einarginatus, Bens. 



17. faba, lair. 



18. flavida, Dunk. 



19. Fortunei, id. 



20. glaberrinia, id. 



21. glandula, Totten. 



Species. 



22. gubemaculum, Dunk. 



23. impacta, Herm. 



24. Japonica, Dunk. 



25. laevigata, Gray. 



26. lignea, Reeve. 



27. Magellanica, Dunk. 



28. mannorata, Forbes. 



29. Metcalfei, Hani. 

 20. modiolus, Linn. 



31. nana, Dunk. 



32. nexa, Gould. 



33. nigra, Gray. 



34. nitens, Carp. 



35. nitida, Hani. 



36. opifex, Say. 



37. pectinula, Gould. 



38. perfragilis, Dunk. 



39. Petagnae, Scacchi. 



40. phaseolina, Phil. 



41. Philippinarum, Hani. 



42. plicata, Gmel. 



43. plicatula, Lam. 



44. recta, Conrad. 



45. rhombea, Berk. 



46. rhomboidea, Hani. 



47. Senhausii, Reeve. 



48. setigera, Dunk. 



49. speciosa, id. 



50. splendens, id. 



51. striatula, Hani. 



52. strigata, id. 



53. subpurpurea, Dunk. 



54. subramosa, Hani. 



55. subsulcata, Dunk. 



56. subtorta, id. 



57. sulcata, Lam. 



58. Trailii, Reeve. 



59. tristis, Dunk. 



60. tulipa, Lam. 



61. undulata, Dunk. 



62. vagina, Zam. 



63. vexillum, Reeve. 



Figure 



Modiola elongata. PI. 29. Fig. 172. 



round-shouldered form, and light texture 



Shell illustrative of the oblong, 



