ASTEROIDEA 



107 



3. The long spines of the fin-Uke membrane (actino -lateral spines) 



do not join those of the neighbouring ray in the interradial 

 mid-line ......... 4 



Actino -lateral spines joining those of the neighbouring ray in the 

 interradial mid -line ....... 5 



4. Paxillae with 6-7 slender, delicate spines 1. H. pellucidus W. Th. 



,, „ 2-3 rather robust spines 2. H. giganteus Sladen 



5. Jaws with 2 lateral spines ; rays appear as a petaloid figure on 



the dorsal side of disk . . . . H. Giboryi Perrier 



Jaws with 4 lateral spines ; rays do not appear as a petaloid 



figure on dorsal side of disk . . . H. roseus Koehler 



1. Hymenaster pellucidus Wyv. Thomson. (Figs. 62 ; 63, 1, 2.) 



Body very flattened, only slightly rising towards the middle ; 

 almost pentagonal, the ends of rays protruding only very little. 

 Paxillse with generally 6-7 (8) slender, delicate spines, scarcely 

 protruding through the membrane. Valves around the central 

 opening with 8-10 long, slender spines. Actino-lateral spines not 



Fig. 62. — Hymenaster pellucidus, oral and dorsal side. Nat. size. 



joining those of neighbouring rays in the interradial mid-line. 

 Jaws with a distinct median projection ; they are broadest 

 behind the middle (Fig. 63, 2). Two, more rarely three, furrow 

 spines, the proximal slightly the larger. Spines of segmental 

 apertures enclosed by an oval sac of thin skin ; the spine itself 

 broad in the basal half and with a single median prolongation 



