0. A. Derby — Stem Structure of Tietea Singularis. 253 



so as to permit the representation of a narrow zone at the front 

 of each. In A the only completely preserved row of F strands 

 is taken as a center and the plotting is continued laterally to 



Fig. 1. 



K 



^oO^fcL.J^I 



1 ^ \.<s^oy ■...: 



<0b(& 



sp 





^ 



s 



O 



Sf 



9 fc 



m 



&/ 



J ^ rrf- ■■' S 



Fig. 1. 1/2 nat. size. 



include a half of the two adjacent rows of F strands, while in 

 B the Fl row is given the central place and is flanked on the 

 right by the complete, on the left by the incomplete row of P 

 strands. In both figures the F strands are drawn in black 



