a. Apical view, showing proportion 



of callus. 

 >• h. Dorsal view. 



c. Ventral view. 



d. Section to show interior. 



.540 ON THE SHELL IN VELATES CONOIDEUS- [JunC 14, 



of w. The cavity extends behind s to the point marked +, and 



therefore far beyond the sutural line (suttcre) ; the outer wall at this 



point is very thin. 

 Figs. 15-29. Vclatea conoideus, Lamk. a, apex ; c, callus ; s, uiyophore, which 



at first is formed by a portion of the paries, but subsequently consists 



solely of the' septum. 

 Fig. 15. Young shell of about 2 whorls, to show the small extent of the callus. 



X 3. 

 16. Young shell of about 3J whorls ^ 

 17 4 



18. „ ,, 4i ,, 



19. „ „ # „ 



20. „ „ over 4^ 

 in which fresh periostracal 

 layer begins to be deposited 

 over the callus. 



(Fig. I6d x2; Fig. 17 ^ X 2; Fig. 18d x I) 



21. Adult shell from the anterior side (f nat. size), to show the relative 



proportion of shell in which the growth is normal to that formed of 

 callus and excavated callus. 



Plate XXXII.i 



Fig. 22fl. Axial section of young shell of about 3 whorls: X8. p.L, peri- 

 ostracal layer ; m.L, middle or crystalhne layer ; i.L, infilling 

 layer ; c, callus. The portions of pre-existing layers belonging to 

 the young shell and included in the present walls are marked by 

 the same letters with the addition of accents. 

 22 b. Portion of the anterior wall further magnified, to show the structui-e 

 p.L and the lines of growth in m.l. 



22 c. Junction of the outer wall and callus on the anterior side of the 



same section. 



23 a. Axial section of a specimen of about 3^ whorls : X 6. 



23 b. Junction of the callus and outer wall on the anterior side, further 



magnified. 



24 a. Axial section of a specimen of 4| whorls : X 3J. 



24 b. Following section of the same, showing actual apex. 

 24 c. Junction of callus and outer wall on the anterior side, further 

 magnified. 



25. Section through adult shell in the plane of the septum, to show the 



connection of the latter with the outer wall. 



26. Section parallel with the preceding a little further in from the aperture 



and viewed in the opposite direction. 



27. Radial section of an adult specimen taken on the side away from the 



aperture and showing the junction of the callus and the outer wall, 

 which consists of layers of former callus. 



28. External ventral surface of adult specimen with the course of the 



component plates of the callus marked out. [From two specimens.] 



29. Internal ventral surface from a specimen in the British Museum 



(Natural History) [Reg. 31977], showing the courseof the component 

 plates and their relation to the septum. 



30. Section of a portion of Neritina crepidularia, Lamk., in the plane of 



the direction of growth, showing the junction of the callus and outer 

 wall of the shell on the side furthest from the aperture (considerably 

 enlarged). 



31. Similar section of Tomostoma neritoides, Desh. (considerably en- 



larged). 



The microstructure of the sections is filled in diagrammatically. 



