GENEEA AND GROUPS OF THE ECHINOIDEA. 95 



line at the ambitus ; subcpnical or depressed dorsally, flattish 

 actinally. 



Apical system large, with an elongate periproct with four or 

 more large triangular plates ; basals large, united j radial plates 

 with a double perforation on the adoral edge. 



Ambulacra narrow, with two vertical rows of primaries on flat 

 scrobicules with well-developed bosses and mamelons, imperforate 

 and non-crenulate, diminishing in size towards the apex and 

 sometimes replaced there by granules. Poriferous zones narrow ; 

 pairs of pores iu arcs near the ambitus and abactinally, some on 

 the flanks of the tubercles, becoming slightly crowded actinally. 

 Plates, primaries near the apex and becoming triple compound 

 plates near the ambitus, consisting of a middle large primary 

 plate and adoral and aboral short demi-plates ; the sutures of 

 the demi-plates and the middle primary bent on the flanks of 

 the tubercle and then directed vertically adorally and aborally. 

 Tentacles heteropodous. 



Interradia with a large bare ornamented median area 

 abactinally, and having the primary tubercles largest at the 

 ambitus and diminishing in size towards the apical system or 

 disappearing, placed on flat scrobicules, imperforate, and without 

 crenulation, surrounded with granules. 



Peristome with small branchial incisions and long tags ; buccal 

 membrane rugose near the teeth, with 10 small buccal plates, 

 covered with pedicellarise and with large disked tentacles, other- 

 wise the membrane is bare. Perignathic girdle slender, ridges 

 broad and low ; the ambulacral processes moderate and usually 

 arched. Teeth keeled. Dowelling occurs between the a^^ical 

 plates and between the interradial plates. Pits with spheridia 

 at the median sutural junctions of the ambulacral plates near the 

 peristome. Pedicellariee with glandular stems. 



The epistromal ornamentation very generally developed ; the 

 furrows and ridges and long lines of granules elongate or not, 

 and in zigzag, by the side of and across the interradial bare spaces, 

 and S-shaped bands occur in some species ; the apical system 

 also ornamented. Spines long, curved, more or less triangular in 

 outline, cellular within, those of some primary tubercles very 

 long, some spathulate. 



Fossil. Eocene : England, Europe, N. America. Oligocene 

 and Miocene : Europe, Asia. 



Becent. Florida, the Caribbean Sea, Bourbon, Philippines, 

 Amboyua, Indian Archipelago. 



