THE STELLEROIDEA 257 



pentagonal. Genera Cheiroptaster, Stiirtz ; Loriolaster, Stiirtz ; (?) Rho- 

 palocoma, Salter. SUB-FAMILY 2. PTERASTERINAE, with a well-developed 

 supra-dorsal membrane, opposite ambulacral plates, and actino-lateral 

 spines. Form pentagonal. Genera Benthaster, Slad. ; Caly piaster, Slad. ; 

 Cryptaster, Per. ; Flexaster, Per. ; Hymenaster, Wyv. Thorns. (Fig. XII.) ; 

 Marsipaster, Slad. ; Myxaster, Per. ; Stemster, Mull. & Tr. ; Retaster, Per. 

 SUB-FAMILY 3. PYTHONASTERINAE, with stellate form, opposite ambulacral 

 ossicles, and rudimentary marsupium formed by five triangular fan-like 

 valves ; no segmental apertures or actino-lateral spines. Genus Mayr- 

 aster, Per. ; I'ythonaster, Slad. 



FAMILY 9. PALASTERISCIDAE. Cryptozonia with the ambulacral 

 ossicles alternate for at least part of the arms. The madreporite is 



FIG. XII. 



Hymenaster jvlhtddvs (after Wyv. Thomson). 



large and ventral in position. Actino-lateral spines are present. The 

 dorsal integument is granular. The form is stellate with small inter- 

 brachial areas. Genera Palasteriscus, Stiirtz ; Echinasterella, Stiirtz. 

 This family is remarkable for the abnormal position of the madreporite, 

 which, unlike that of recent Asteroids, is ventral in position. This char- 

 acter is possibly due to the development of a granular integument over 

 the whole of the abactinal surface. Large spine-like paxillae occur, and 

 it is quite possible that the granular integument was the roof of a large 

 marsupium. There can be no question as to the position of the madre- 

 porite, for the actinal and abactinal surfaces of the same specimen are 

 shown in examples in the British Museum. 



FAMILY 10. ECHINASTERIDAE. Cryptozonia with a reticulate abac- 

 tinal skeleton of small imbricating plates. Ambulacral ossicles opposite ; 

 the pores biserial ; oral armament adambulacral. Interbrachial septa 



17 



