HEXACTINELLIDA 



203, 



96). The former set of genera constitute the sub-class Amphi- 

 discophora, the latter / 



the Hexasterophora. 



Sub-Class 1. Am- 

 phidiscophora. — Am - 



phidiscs are present, 

 hexasters absent. A 

 tuft of rooting spicules 

 or hasalia is always 

 present. The ciliated 

 chamiers deviate 7nore 

 or less from the typical 

 thimhle shape, and the 

 membrana reticularis 

 is continuous from 

 chamber to chamber 

 (Figs. 94, 95, 97). 



Flo. ytf. — Hexasters. 

 B, floricome ; 



genera, which may be 



Fig. 95. — Portion of hody-wall oi llyalonema, in 

 section, showing the irregular chambers. 



Sub -Class 2. Hexastero- 

 phora. — Hexasters are present, 

 amphidiscs absent. The cham- 

 bers have the typicalregula,rform, 

 and are sharply marked off from 

 one another (Figs. 90, 96). 



All the Amphidiscophora 

 have Lyssacine skeletons ; in 

 the Hexasterophora both types 

 of skeleton occur. The sub- 

 division of the Hexasterophora 

 is determined by the presence 

 nr absence of uncinate spicules. 

 An " unciiiatum " is a diactine 

 spicule, pointed at both ends 

 and bearing barbs all directed 

 towards one end. This method 

 of classification gives us a 

 wholly Dictyonine order, 

 Uncinataria, and an order 

 consisting partly of Dictyo- 

 nine, partly of Lyssacine 

 distinguished as the Anuncinatakia. 



A, Graph iohexaster ; 

 C, onychaster. 



