236 



NEW YORK STATi: MUSEUM 



IMaking- a i^encral review of the differences in rate of growth 

 already recorded we may say that the vertical element was strong 

 throughout the three circlets of plates, except on the orad ends of 

 the RR and the aborad ends of the IBB, but that the lateral ele- 

 ment was exceedingly w^eak near the proximal stem joint and 

 gradually became stronger on ascent of the cup. At the base of 

 the arms it very nearly equalled the rate of the vertical element, 

 llie cup thus received its present fusiform character. 



The orad intcrradial scries. There remain five b.vs. not yet 

 accounted for and these apparently had their points of origin at the 

 orad ends of the sutures between the RR. Each member of the 



Fig. 15 



Fig. 16 



VAVA^V 



series seems to have had no room for further development but the 

 position is so close to the arms that the series may be connected with 

 the more elaborate respiratory system of the latter. 



Relations of the b.z's. The relations of the four classes of 

 groups as we have interpreted them may be shown by text figure 15, 



