HEXACTINELLIDA 



xn- 



96). The former set of 

 discopliora, the latter 

 the Hexasterophora. 



Sub-Class 1. Am- 

 phidiscophora. — Ayyi- 

 phidiscs are present, 

 hexasters absent. A 

 tvft of rooting spicules 

 or hasalia is always 

 present. The ciliafti^ 

 chambers deviate mar' 

 or less from the typical -^S 

 thiinble shap)e, and the 

 membrana reticidaris 

 is continuous from 

 chamber to chamber 

 (Figs. 94, 95, 97). 



genera ci institute tlie sub-class Aniplii- 



-^M/ 





FiL.. yt).— Hexasters. 

 B, Horicome ; 



A, GrapliioliL'xastcr 

 C, onychaster. 



genera, wliich niav he distin; 



Fig. 95. — Portion ol Ijody-wall of llyolonema, 

 section, showing tlie irregular chambers. 



Sub -Class 2. Hexastero- 

 phora. — Hexasters are present, 

 ainphidiscs absent. The cham- 

 bers have the typiccdregidarform . 

 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 tlie Hexasterophora 

 is determined by the presence 

 or absence of uncinate spicules. 

 An " uncinatum " 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 

 uished as the AxUNCTNATARIA. 



