202 



p. HERBERT CARPENTER. 



represented by the letters B, R, and O respectively, their 

 relative positions just after the appearance of the radials are 

 represented in fig. 15. The line separating RE. and O in- 

 dicates the position of the above-mentioned equatorial zone 

 separating the oral system developed around the left perito- 

 neal sac, from the calyx which is formed around that of the 



Tig. XV. — Diagram showing the relative positions of the basals, orals, 

 and radials, in an early stage of the development of a Crinoid. B. 

 Basal. O. Oral. E,. Kadial. Eq, Line indicating the position 

 of the equatorial zone which separates the oral and apical systems. 



right side (compare figs, i, viii, ix in Part I). Fig. xvi shows 

 the mode in which the supra-radial antiambulacral skeleton 



NX" 



Fig. xvi. — Diagram showing the relations of the apical and oral systems 

 in an adult Crinoid. 'BOB. as in Fig. XV. B. B3. Second 

 and third radials. 



of the arms of a Crinoid is formed in support of a lateral ex- 

 tension of tlio equatorial zone. In the t3rchins and Holo- 



FiG. XVIL — Diagram showing the relative positions of the basals, orals, 

 and radials iu Leskia mirabilis. Lettering as in Fig. XV. 



thurians, however, the extension of the equatorial zone is in 

 a vertical direction (fig. xvii) , and in the former it becomes 

 covered by a superambulacral plating, which extends over on 

 to it from the abactinal side. 



In the Starfishes (fig. xviii) the radials are carried out from 



