PLATE XXII. 



1. A piece of the upper part of the stem of Plate XVIII. Fig. 3. 



2. Three rings of the same, more magnified, showing the extremities of the wedge-shaped lobes of the 



young joints forcing their way between the flat and the ribbed joints. 



3. Proximal face of one of the ribbed rings of Fig. 2. 



4. Distal face of the same ring. 



5. Segment of proximal face of young stem joint fitting upon face of Fig. 4. 



6. Segment of the distal face of a similar younger joint of an adjoining ring. 



7. Reticulation from the centre to the base of the ribs. 



8. Indistinct pentagon forming opening for axial cord. 



9. Reticulation round the axial ring. 



