252 THE STELLEROIDEA 



Spatangoids (see p. 319). In Ctetiodiscus the grooves between the marginal 

 ossicles are bordered by bands of lamellae forming the simplest type of 

 cribriform organs. In the rest of the Porcellanasteridae these organs are 

 confined to a few special plates. In some species of this family the 

 anus opens on the summit of a small tube. It rises from the abactinal 

 surface of the starfish, and has been accordingly compared to the stem 

 of Crinoids, an homology which is quite inadmissible. 



FAMILY 7. ASTROPECTIXIDAE. Phanerozonia with opposite ambula- 

 cral plates and paxilliform abactinal plates. Super-ambulacral plates are 

 present, and the adambulacral plates are compressed. There is no anus, 

 and pedicellariae are rarely present. The compressed adambulacral plates 

 and the presence of a series of super-ami mlacral plates, which occur inside 



Fie;. VIII. 

 Porcdlanastcr cacrulcus. Abactinal surface showing cribriform organs and anal tube. 



the arms above the ambulacrals, are the two most striking features of 

 the Astropectinidae. The position of the super-ambulacral plates is 

 shown in Fig. VII. There are two sub -families and nine genera. 

 SUB-FAMILY 1. ASTROPECTININAE, including those members of the family 

 in which the adambulacral plates touch the infero- marginal plates 

 along the ray. The marginal and adambulacral plates do not correspond 

 in length or number. Genera Astropertea, Schul/e ; Bathybiaster, 

 Danielssen and Koren ; Craspidaster, Slad. ; Dipsacaster, Alcock ; Blakiastcr, 

 Per. (syn. Leptoptychaster, Smith), (Fig. IX.) ; Moriatter, Phoraster, and 

 Psilaster, Sladen. SUB-FAMILY 2. LUIDIINAE. Astropectinidae with a 

 row of small plates separating the adambulacral and infero- marginal 

 plates. Genera Astrdhi, Per. ; Luidia, Forbes ; Platasterias, Gray. 



FAMILY 8. PENTAGONASTKRIDAE. Phanero/onia with opposite ambu- 

 Incral plates, large marginal plates, and tessc-llate abactinal skeleton. 



