4 PEor. p. M. Duncan's revision of the 



Sul)kingdom ECHINODERMATA. 



Class ECHINOIDEA. 



Echinodermata with a solid or slightly flexible test covering the 

 viscera, variable in sbape from spheroidal to flat, composed of 

 numerous, closely placed, more or less geometrical plates of car- 

 bonate of lime, covered with soft structures and carrying spines. 

 Most of the plates arranged in several vertical series, reaching 

 from the mouth to the dorso-central or apical system, constituting 

 five ambulacral and five interradial areas. Other plates in the 

 dorso-central system — the basal and radial and anal plates. "With 

 a mouth on the under or actinal surface, rarely in front of the 

 test, and an internal gullet and intestinal tract ending externally 

 in an anus, which is either placed in the dorso-central system or 

 somewhere in the posterior interradium. A madreporite body 

 placed in the dorso-central system and in relation with a renal 

 organ and with the water-system, which is partly within the test 

 and partly external, in the form of branchige and branchial 

 tentacles. With or without five teeth in jaw-pieces, which are 

 moved by muscles connected with a connected or disconnected 

 perignathic girdle. 



Unisexual or bisexual ; the genital glands with ducts perforating 

 the basal plates or opening beyond them ; the young, either under- 

 going metamorphoses and being free-swimmers, or found perfect 

 upon the parent's test. 



Marine : fossil and recent. 



I. Subclass. The Paljeeohinoidea, Zittel (amended). 

 Echinoidea with only one, or with more than two, vertical rows 

 of plates in each of the five interradia, and with either tvvo or 

 many vertical rows of simple or compound plates in each of the 

 five ambulacra ; plates of the areas overlapping or not. Peristome 

 actinal. Jaws present. Periproct within the dorso-central 

 system or in the posterior interradium beyond. 



II. Subclass. The Euechinoidea, Bronn. 

 Echinoidea with two vertical rows of plates in each of the five 

 interradia, and a similar number of vertical rows of simple or of 

 compound plates in each of the five ambulacra. Peristome actinal, 



