OENEEA AISTD GROUPS OF THE ECHINOIDEA. 117 



as nine components each perforated by a pair of pores ; the aboral 

 plate a small primary, tlie adoral a large primary, all the others 

 demi-plates ; pairs of pores polyserial actinally. 



Interradia with few coronal plates, very narrow actinally, each 

 plate with a large plain tubercle resembling the ambulacral, 

 diminishing in size from the ambitus ; secondary tubercles 

 abundant. 



Peristome large ; branchial incisions broad ; perignathic girdle 

 well developed. Jaws with a tall narrow foramen ; teeth keeled. 

 Buccal plates large, spined, and with pedicellarise. Spines very 

 large, stout, long, flat, oar-shaped, or triangular in transverse 

 section ; secondary spines short, either forming a pavement around 

 the primaries with their inflated ends, or sharp and pointed in 

 the same position. 



Becent. Red Sea to Sandwich Islands, Piji, Mauritius, Java, 

 New Caledonia, Australia. Of late years one species, S. mamil- 

 lafus, has made its way from the Eed Sea, via the Suez Canal, 

 into the Mediterranean. 



Genus Colobocenteottjs, Brandt (subgenus), 1834, Prodr. Desc. 

 Anim. p. 266 ; Bee. d. VActes de VAcad. St. Petersb. {Ad- 

 ditions), 1834-35. A. Agassiz, 1872-74, Bevision, p. 423. 

 Loven, Etudes, 1874, p. 26 ; 1887, Ech. descr. hy Linnceus, 

 p. 158. J. Bell, 1881, Proc. Zool. Soe. p. 421. 

 Syn. Echinus (pars), Linnaeus ; Cidaris (pars), Leske ; EcM- 

 nometra, Grray, 1825 ; Podopliora, Agass. 



Test thick, moderate in size, elliptical or subcircular in rather 

 tumid marginal outline, subcorneal, tumid, or depressed hemi- 

 spherical abactinally ; more or less concave, with a comparatively 

 flat surface actinally ; elongate transversely ; the antero-posterior 

 axis is shorter than the transverse, which passes through amb. II. 

 and IV. 



Apical system central ; periproct small, with small plates ; basal 

 plates large, with primary and secondary tubercles upon them ; 

 radial plates excluded, small, with a tubercle, and the pore large 

 and adoral. 



Ambulacra straight, very broad actinally -, plates high, com- 

 posed of a small aboral primary, a large adoral primary, and from 

 three to many intermediate small demi-plates ; poriferous zones 

 wide, and containing arcs of many pairs of pores separated and 



