ABATUS ca\t:rxosls. 



213 



There are five spheridia near the actinostome, one in each ambulacral 

 area (PI. 99, fig. l). 



Each interambulacrum has one actinal plate followed by four and a half 

 coronal plates carrying on each plate from one to six primary and secondary 

 tubercles. The ambulacral areas are bare. In older specimens * 3 mm. in 

 length there is a miliary in each ambulacral plate. 



Op 



5 » 



1.6 mm. 



Fig. 307. A. cavernosus. 



Loven is right in objecting to the association of Ahaius cavernosus Trosch. 

 with Hemiaster.- The structure of the abactinal system of Hemia<ter ia 



abb 



37 til 111 



FiQ. 309. A. CAvEKNosus. Fig. 310. Hemiaster bcfo. 



Ajtkk Jjo-rts. 



37 Tntw 



Fig. oil. Abatus cavkbxosvs. 



of an ancient type, Fig. 310. while that of Abatus is eminently Schizas- 

 teroid, Fig. 311 (PI. 99, fig. .9), but neither Troschel nor myself had noticed 

 the difference in the structure of the abactinal system of Abatus and Heini- 

 a;>ter first detected by Loven. 



1 "Challenger " Echinoidea PI. XX», figs. 9. 10. « Pourtalesia. p. 72. 



