314 



COMPARATIVE ANATOMY 



Sub-Class 3. Blastoidea. 



Armless Pelniatozoa, either pear-shaped, club-sliaped, oviform, or si)herical. 

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



Fig. l'63.— Pentremites, from 

 the side, without pinnules. 1, 

 Interradial = deltoid ; 2, 3, radials ; 

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

 acle. 



Fig. 205— Codaster bilobatus. M'Coy, from the oral 

 side (after Etheridge and Carpenter). 1, Hydrospin- 

 slits ; 2, lateral plates ; 3, ambulacra! groove ; 4, mouth : 

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

 radial ; 9, ridge on an interradial. 



Fig. 264. — Granatocrinus Norwoodi 

 (after Etheridge and Carpenter); fnim 

 the apical side, with stem. 



Fig. 266.— Orophocrinus stelliformis (after Ethe- 

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

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

 spire slits ; 4, anus ; 5. ambulaeral groove ; 0, points 

 of attachment of the pinnules. 



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

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



