296 



COMPARATIVE ANATOMY 



CHAP. 



SUB-CLASS 2. Euasteroidea. 

 Asteroidea with paired, i.e. opposite ambnlacral plates or " vertebrse." 



Order 1. Phanerozonia. 



Asteroidea with large, strongly developed, marginal plates. The inframarginal 

 and supramarginal plates are closely fitted together. Papulae (branchial vesicles) 

 only occur on that surface of the body which is surrounded by the supramarginal 



FIG. 239. Ctenodiscus procurator (after Sladen), from the oral side. A Gastropod in the 

 stomach is visible through the mouth. 



plates, i.e. on the apical or upper side. Ambulacral plates broad. In each ambu- 

 lacral furrow there are two longitudinal rows of tube-feet. The adambulacral plates 

 are prominent in the oral skeleton. Where pedicellarise occur they are sessile. 



Fam. 1. Archasteridse : Parar chaster, Dy taster, Plutonaster, Pseudar chaster, 

 Archaster, etc. Fam. 2. Porcellanasteridse, the centre of the apical system pro- 

 duced into a more or less long outgrowth : Porcellaviaster, Hyplmlaster , Ctenodiscus 

 (Fig. 239), etc. Fam. 3. Astropectinidse, without anus and usually without pedicel- 

 larise : Astropecten, BathyUaster, lly aster, Luidia, etc. Fam. 4. Pentagonasteridae : 

 Pentagonaster, Astrogonium, Nectria, Calliaster, Stellaster, Goniodiscus, Mimaster, etc. 

 Fam. 5. Antheneidae : Anthenea (Fig. 240), Goniaster, etc. Fam. 6. Pentacerotidae : 



