296 



COMPARATIVE ANATOMY 



CHAP. 



Sub-Class 2. Euasteroidea. 

 Asteroidea with paired, i.e. opposite ambulacral plates or " vertebra;." 



Order 1. Phanerozonia. 



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

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

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



FiQ. 239. — Ctenodiscus procurator (after Sladen), from the oral side. A Ga.stropod 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 adambulaoral plates 

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



Fam. 1. Archasteridse : Pararchaster, Dytaster, Plutnaaster, Pseudarchastcr, 

 Archctster, etc. Fam. 2. Porcellanasteridse, the centre of the apical S3'stem pro- 

 duced into a more or less long oittgrowth : Porcellanaster, Hyphalastcr, Ctenodiscus 

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

 larisE : Aslropecten, Sathybiaster, llyaster, Luiella, etc. Fam. 4. Pentagonasteridae : 

 Prittagmiaskr, Astroguaium, Neclria, CalliasUr, Stellaster, Honindiseus, Mimaster, etc. 

 Fam. 5. Antheneidse : Anthenea (Fig. 240), Gnnldster, etc. Fam. 6. Pentacerotidse : 



