CLASS I 



ECHINOIDEA 



281 



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

 crowded and triserial below the ambitus. Both areas with two vertical rows 

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

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



Family 4. Arbaciidae Gray. 



Amhulacral plates compound. Primordial interamhulacral plates in the hasi- 

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

 in the sequence F, I, IF. Periproct with four or Jive large plates only. Primary 

 tubercles imperforate. No spurs from pyramids supporting teeth dorsally. Tertiary 

 to Recent. 



Arbacia Gray. With three elements in an ambulacral plate. Tertiarj' 

 and Recent. 



TetrapygiLS Agassiz. With five elements in an ambulacral plate. Recent. 



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

 rows of plain, 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 anfl Recent. 



Podocidaris A. Agassiz. Recent ; Caribbean Sea and 

 Philipi^ines. 



Fid. 395. 



Coelufilenrus oquis Ag. 

 Eocene : Biarritz, France. 



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 F, I or I, F, IF, II, III. Periproct usually plated 

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

 Peristome tvith 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. Cretaceous to Recent. 



Family 1. Echinidae Agassiz. 



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

 Ambulacral plates at mid-zone composed of three elements each, rarely dorsally 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, plain, primary tubercles with or without irregularly placed 

 secondary tubercles and primaries. I Amb with two vertical rows of primaries, 

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

 small, circular. Cretaceous to Recent. 



