into three parts. The cross-lines, representing the natunil size of the 

 specimen, are too short. 



Figure 8rt. — Outline profile of the same. 



Figure 9. — Cardinal view at a size of 12 X H nini. The ventral 

 valve and area have become greatly curved, and the dorsal apci tnre is 

 (]uite filled by the tripartite cardinal process. 



Figure 9a. — Outline profile of the same. 



Figure 10. — Cardinal view of a large adult; size 18 X IS.") mm. 

 The areas are closely apjn-essed, and the dorsal aperture is wholly filled 

 by the cardinal process, the central portion of which extends into the 

 aperture of the other valve. 



Figure lOrt. — Outline profile of the same. 



Figure 11. — Cardinal view of a normal adult; natural size. 



Figure 11a. — Profile of the same. (op. cit., pi. 21, figs. 17, 11.) 



Figure 12. — Dorsal view of a small adult. 



Figure 12a. — Ventral view of the same. (op. cit.. figs. 12, 11.) 



RIIIPIDOMELLA IIYBRIDA Sowerby (Pages 321, 322) 



Figure 13. — Cardinal view of a veiy young individual having a length 

 of 1 mm. and a width of 1.5 mm. The valves are nearly equi-convex, the 

 area and apertures as in tlie earlier stages of D. elegantula. 



Figure 13a. — Outline profile of the same. 



Figure 14. — Cardinal view of a somewhat gibbous example measur- 

 ing 10 X 8 mm. The relatively short areas are about equally developed, 

 and the cardinal callosity of the dorsal valve has already filled the dorsal 

 aperture. 



Figure 14a. — Outlini' profile of the same. 



Figure 15. — Cardinal view of a normal adult 12 X 10 mm. ; showing 

 tlie short area and the projection of the cardinal process into the ventral 

 aperture. 



Figure 15a. — Outline profile ; showing the incurvature of the areas. 



Figure 1G. — Dorsal view of a large adult, (op. cit, fig. 20.) 



Figure 17. — Profile of a normal adult, (op. cit., fig. 21.) 



Figure 18. — Dorsal view of a small, gil)bous exanqile ; showing 

 strong varices. Enlarged to two diameters. 



Figure 18a. — Profile of the same. 



