314 



COMPARATIVE ANATOMY 



CHAP. 



SUB-CLASS 3. Blastoidea. 



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

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



FIG. 2(53. Pentremites, from FIG. 2t>5. Codaster bilobatus. M'Coy, from the oral 



the side, without pinnules. 1, side, (after Etheridge and Carpenter). 1, Hydrospiiv 



Interradial = deltoid ; 2, 3, radials ; slits; 2, lateral plates; 3, ambulacral groove; 4, mouth; 



4, basal ; 5, ambulacrum : f<. spir- 5, radial ; ti, suture between two radials; 7. anus; S, inter- 



acle. radial ; 0, ridge on an interradial. 



Fio. -264. Granatocrinus Norwood! 

 (after Etheridge and Carpenter): fn.m Fro. 266.-OrophoorimiB Stelllfonnls (after Ethe- 



the apical side, with stem. ridge ^' l Carpenter) ; from th,- oral side. 1. Lateral 



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

 spire slits ; 4, anus ; f>. ambulacral groove ; 0, 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 



