314 



COMPARATIVE ANATOMY 



CHAP. 



SUB-CLASS 3. Blastoidea. 



Armless Pelmatozoa, either pear-shaped, club-shaped, oviform, or spherical. 

 Body usually regularly radiate. Base mouocyclic. Three basals, one small and 



FIG. 263. Pentremites, from 

 the side, without pinnules. 1, 

 Interradial = deltoid ; 2, 3, radials ; 

 4, basal ; 5, ambulacrum ; 6, spir- 

 acle. 



FIG. 265. Codaster bilobatus, M'Coy, from the oral 

 side (after Etheridge and Carpenter). 1, Hydrospiiv 

 slits ; 2, lateral plates ; 3, ambulacral groove ; 4, mouth ; 

 5, radial ; 6, suture between two radials; 7, anus; 8, inter- 

 radial ; 9, ridge on an interradial. 



Fio. 264. Granatocrinus Norwood! 

 (after Etheridge and Carpenter); from FIG. 266.-Orophocrinus stelliformis (after Ethe- 



the apical side, with stem. ridge and Carpenter) ; from the oral side. 1, Lateral 



plates ; 2, covering plates of the ambulacra ; 3, hydro- 

 spire slits ; 4, anus ; 5. ambulacral groove ; 6, points 

 of attachment of the pinnules. 



two larger. Five radials, more or less deeply cut out for the reception of the five 

 ambulacra. Five interradials lying above the five radials, and surrounding the 



