DESCRIPTION. 133 



Fig. 4.0. Folium. 



Shell ovate, obtusely plaited at the sides, para- 

 sitical. 



D' Argeiiville Conch, t. 19. F. 



Specimen pale purplish brown, underneath in- 

 clining to white; hinge with a triangular sinus ; 

 upper valve turgid towards the middle, rough and 

 transversely ribbed on both sides ; lower valve 

 smaller, flat, and channelled through the middle. 



Inhabits the Indian Ocean. 



Fig. 5. O. Isogonum. 



Shell equivalve, lobed, the larger lobe at right 

 angles to the hinge. 



Bumph. Mus. tab. 47.1. 



Specimen inclining to violet, with shades of 

 black, within pearly; lamellate; beak unclosed. 



Inhabits the Indian Ocean and South Seas. 



PLATE X. 



Fig. 1. Anomia vitrea. 



Shell nearly orbicular, ventricose, hyaline, ex- 

 tremely thin ; lower valve with two bony rays at 



