RADIATA. ECHINODERMATA. 
m 
I.---ECHmODERMATA. 
Order I. -—Free. 
Sect. I. — Locomotion executed by means of suckers. These 
consist of tubular extensile processes , with a terminal, usually 
fringed disc, which serves either as an organ of motion or rest; 
the central canal admitting water to the aerating organs. 
A. Covering of immoveable testaceous plates, without projecting 
arms. Echinid.®. 
A A. Covering crustaceous and moveable. 
a. Body produced. Fistulidm. 
a a. Body depressed, or orbicular, and divided into arms or 
rays. Asteriadce. 
Sect. II. — -Destitute of suckers for locomotion. 
Sipunculus. 
Priapulus. 
Order II. — Fixed; the body covered by articulating plates, 
supported by an articulated column. 
Crinoidse. Margin of the oral disc supporting numerous articu- 
lated arms. 
Blastoidae. Margin of the oral disc destitute of arms ; body with 
avenues of branchial pores. 
