SYSTEMATIC CLASSIFICATION OF ECHINI. 203 



four, or five large plates only. Peristome with ten primordial amhulacral, also non- 

 aiiiliulacral plates. Lantern erect. Primary tubercles imperforate, or exceptionally 



perforate Suborder S 77iiO£>O.V 7'. 1. 



Ambulacral plates compound, or largely simple. Primordial interambulacral 

 plates resorbed. Base of corona resorbed. Oculars exsert or becoming insert 

 in the .seciuence I, V, IV, II, III. Periproct with a permanent large suranal, 

 or more large plates, with small anal plates. Primary tubercles imperforate, 

 or perforate. No spurs from pyramids supporting teeth. 



Family Saleniidae. 



Ambulacral plates compound. Primordial interambulacral plates resorbed. 

 Base of corona resorbed. Oculars becoming insert in the sequence I, V, IV, II, 

 III. Periproct with numerous small plates only. Primary tubercles imperforate. 

 Spurs from pyramids support the teeth dorsally. . Family Phymosomatidae. 

 Ambulacral plates compound, composed of three elements each, at the mid-zone 

 every four or five ambulacral plates are bound together and grown over by one 

 primary tubercle. Primordial interambulacral plates resorbed. Base of corona 

 resorbed. Oculars becoming insert in the sequence I, V, IV. Periproct with 

 many small plates only. Primary tubercles imperforate. Spurs from pyramids 



support the teeth dorsally Family Stomopneustidae. 



Ambulacral plates compound. Primordial interambulacral plates in the basi- 

 coronal row. Base of corona not resorbed. Oculars all exsert or becoming insert 

 in the sequence V, I, IV. Periproct with four or fi\e large plates only. Primary 

 tubercles imperforate. No spurs from pyramids supporting teeth. 



Family Arbaciidae. . 

 EE. Epiphyses wide, meeting in suture over the foramen magnum. Ambulacral 

 plates compound. Coronal plates not imbricate. Ambitus circular, or elliptical 

 through a sidewise axis. Primordial interambulacral plates resorbed. Base of 

 corona resorbed. Oculars all exsert or becoming insert in the sequence V, I or I, 

 V, IV, II, III. Periproct usually plated witli many small plates (in one genus, 

 Parasalenia, with four large plates). Peristome with ten (in one species five) 

 primordial ambulacral plates and more or fewer non-ambulacral plates; rarely 

 the latter are absent. Lantern erect. Primary tubercles imperforate. 



Suborder CAMARODONTA. 



Ambitus circular. Pits, or sculpturing in coronal plates dorsally. Ambulacral 

 plates at mid-zone composed of three elements each. Oculars usually all exsert. 



Family Temnopleuridae. 



Ambitus circular. No pits or sculpturing in coronal plates dorsally. Ambula- 

 cral plates at mid-zone composed of tliree elements each, rarely dorsally 

 of two elements. Oculars all exsert, or becoming insert in the sequence I, V, 

 IV, II, III Family Echinidae. 



Ambitus circular. No pits or sculpturing in the coronal plates. Ambulacral 



