34 A SYNOPSIS OF ANIMAL CLASSIFICATION. 



Around the mouth is a crown of 

 fringed, retractile tentacles. Lar- 

 val form the Auricularia. 



Order i . Pedata Ambulacral feet present. 



X Peniacta, Thyone. 



Order 2. Apoda Ambulacral feet wanting. 



X Synapia. 



Class II. ASTEROIDEA Star-shaped to pentagonal Echino- 



derms, with exo-skeleton in the 

 form of a rough net-work studded 

 with short fixed spines. Ambu- 

 lacral feet in grooves on oral side. 



Order i. Asteridea No definite boundary between disc 



and arms; larval forms the Bipin- 

 naria and Brachiolaria. 



Order 2, Ophiuridea Disc and arms distinct, the latter 



serpentine and very brittle. Lar- 

 val form a Pluteus, similar to that 

 of Class IV. 



Class III. CRirrOIDEA Sessile forms, somewhat resem- 

 bling Ophiuridea on stalks. The 

 part corresponding to the disc of 

 the latter is here called the calyx 

 and is so placed that the mouth is 

 above, surrounded by the many 

 branched arms. Larval form oval 

 in form, with ciliated bands run- 

 ning around it. 



Class IV. ECHINOIDEA Spheroidal, oval, or disc-shaped 



forms, with extensive exo-skeleton 

 composed of large calcareous plates 

 arranged in meridional rows, and 

 beset with movable spines. The 

 ambulacral feet project from foram- 

 ina in the plates of certain rows, 

 called ambulacral. Larval form 

 a Pluteus. 



