CLASS I 



ECHINOIDEA 



281 



Stomopneustes Ag. Am,h straight, with pores in arcs of three pairs dorsally 

 crowded and triserial below the ambitiis. Both aieas with two vertical rows 

 of piain tubercles. Formerly classed with the Echinometridae, from which it 

 diifers radically, especially in structure of the lantern. Tertiary and Recent. 



Family 4. Arbaciidae Gray. 



Ambulacral plates Compound, 

 coronal row. Base of Corona not 



Primordial interambulacral plates in the basi- 

 resorhed. Oculars all exsert or becoming insert 



IV. Periproct with four or five large plates only. 

 No spurs from pyramids supporting teeth dorsally. 



Primary 

 Tertiary 



With three elements in an ambulacral plate. Tertiary 



Recent. 



in the sequence V, I, 

 tubercles imperforate. 

 to Kecent. 



Arbacia Gray, 

 and Recent. 



Tetrapygiis Agassiz. With five elements in an ambulacral plate 



Coelopleurus Ag. (Fig. 395). Amb with two vertical 

 rows of piain, primary tubercles placed on flat scrobi- 

 cules, diminishing in size toward the apex, and some- 

 times replaced there by granules. lAmb with a large 

 bare median area abactinally ; the tubercles largest at 

 the ambitus, sometimes disappearing toward the apical 

 System. Tertiary and Recent. 



Podocidaris A. Agassiz. Recent ; Caribbean Sea and 

 Philippines. 



Suborder C. CAMARODONTA Jackson. 



Teeth keeled. Epiphyses wide, meeting in suture over 

 the foramen magnum. Ambulacral plates Compound. Coronal 

 plates not imbricate. The ambitus is 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, F, IF, II, III. Periproct usnally plated 

 with many small plates {in one genus, Parasalenia, with four large plates). 

 Peristome with ten {in one species five) primordial ambulacral plates and rnore or 

 fewer non-ambulacral plates ; rarely the latter are absent. Lantern erect. Primary 

 tubercles imperforate. Cretaceous to Recent. 



Fig. 395. 



Coeloplewus equis Ag. 

 Eocene ; Biarritz, France. 



Family 1. Eohinidae Agassiz. 



Ambitus circular. A^o pits or sculpturing in the coronal plates dorsally. 

 Ambulacral plates at mid-zone composed of three elements each, rarely darsally of 

 two elements. Oculars all exsert, or becoming insert in the sequence I, F, IF, II, 

 III. Cretaceous to Recent. 



Echinus Linn. Amb straight, with narrow poriferous zones ; pore-pairs in 

 more or less vertical arcs of triplets. Interporiferous areas with two vertical 

 rows of small, piain, primary tubercles with or without irregularly placed 

 secondary tubercles and primaries. lAmb with two vertical rows of primaries, 

 and few or numerous rows of secondary tubercles and miliaries. Peristome 

 small, circular. Cretaceous to Recent. 



