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ECHINODERMATA. 



No shell ; nor any calcareous pieces in 

 the leathery skin ; no calcareous ring 

 around the gullet ; body \ cylindrical ; 

 locomotion 'by alternate contraction and 

 extension of the body 



Order I. ECHINOIDEA. 



Mouth below ; vent above ; both cen- 

 tral ; avenues 5, continuous from the 

 vent to the mouth ; ovaries 5 ; a complex 

 apparatus of teeth Cidaridce. 



Mouth and vent below; the mouth 

 central, armed with teeth ; avenues not 

 continuous ; ovaries 5 Clypeasterida. 



Mouth below, not central ; vent at one 

 side ; avenues not continuous ; ovaries 

 4 ; no teeth Spatangida. 



FAMILY I. CIDARID.E. 

 Cidaris (Leske). Body globose; vent and 



