36 



obvious and characteristic assemblages of shells as refer to the genera in 

 question, though differing in no other respect, are equally entitled to generic 

 distinction. A system of arrangement based upon the characters of the 

 soft parts of the mollusk alone, without reference to the shell or hard parts, 

 is scarcely less objectionable than one founded upon the shell alone, without 

 reference to the organic structure of the animal. 



The shell of Ovulum differs from that of Cypma in having the extremities 

 more or less prolonged, and in the lip and columella being destitute of the 

 prominent rows of teeth with which that genus is so remarkably charac- 

 terized ; the outer lip, as in the 0. ovum and imperialis is in one or two in- 

 stances a little wrinkled, but never toothed. Another distinction consists in 

 the Ovulum not being provided with any pattern or design of colour, nor with 

 colour in any form beyond a faint tinge of pink, violet, or yellow. 



The genus Ovulum is somewhat limited in species, and they are mostly 

 small ; the 0. ovum is the only one of large size, and the 0. imperialis the 

 only species of intermediate size ; the well-known Chinese species, the 0. 

 volva, presents a remarkable example of prolongation of the extremities, and 

 the 0. verrucosa, the nearest approach to Cypnea, is characterized by the 

 presence of two small wart-like callosities like those of the C. bicallosa. 



1. aciculare, Sow. 



2. Adriaticum, Sow. 



3. aequale, Sow. 



4. album, Dufo. 



5. avena, Sow. 



6. birostre, Lam. 



7. breve, Sow. 



8. cameum, Lam. 



9. corrugatum, Hinds. 



10. dorsuosum, Hinds. 



11. emarginatum, Sow. 



12. formicarium, Sow. 



Species. 



13. frumentum, Soto. 



14. galhnaceum. Hinds. 



15. gibbosum, Lam. 



16. hordeaceum, Lam. 



17. inflexum, Soiv. 



18. intermedium, Sow. 



19. lacteum, Lam. 



20. longirostratum, Sow. 



21. margarita, Sow. 



22. marginatum, Sow. 



23. nigerinum, Dufo. 



24. obtusum, Sow. 



Figures. 



25. ovum, Soto. 



26. patulum, Sow. 



27. pyriforme, Sow. 



28. rufum, Sow. 



29. secale, Sow. 



30. seminulum, Sow. 



31. spelta, Lam. 



32. striatulum, Sow. 



33. tortile, Des. 



34. triticeum, Lam. 



35. verrucosa, Sow. 



36. volva, Lam. 



Ovulum ovum. Plate F— Fig. 3. Shell with animal, showing the ex- 

 panded disc, in slight folds ; the right lobe of the mantle with its 

 spinous processes partially extended ; the broad wrinkled siphonal ap- 

 pendage; the tentacles proceeding from the concealed head; and the 

 eyes on the thickened part of the tentacles. From the Zoology of the 

 I <>//age de I' Astrolabe. 



< >vulum volva. Plate 1. Fig. 5.— Shell. From Mr. Cuming's collection. 



