SYSTEMATIC CLASSIFICATION OF ECHINI. 207 



interambulacral area. Plates not imbricate, but ambulacral plates bevel over the 

 interambulacral on adradial sutures. Primordial interambulacral plates resorbed. 

 One row only of interambulacral plates resorbed in advance of the peristome. 

 Oculars usually all insert, genitals usually with three to five pores each. Peri- 

 stome with many rows of ambulacral ami some interradial non-ambulacral plates 

 (Plate 5(5, figs. 7, 8). Secondary spines and imperforate tubercles only. 



Family Pal,\eechinidae. 



Two columns of plates in each ambulacral area, consisting of plates which are 



all primaries; pore-pairs uniserial. Four to six columns of plates in each 



interambulacral area Palaeechinus (four species). 



Two columns of plates in each ambulacral area, consisting of plates which are 

 alternately primaries and partially or completely occluded; pore-pairs biserial. 

 Four to eight, or nine columns of plates in each interambulacral area. 



Maccoya (six species). 

 Four columns of plates in each ambulacral area, consisting of demi- and occluded 

 plates; pore-pairs biserial. Four to seven columns of plates in each inter- 

 ambulacral area. Lovenechimis (six species). 



F<iur columns of plates in each ambulacral area, consisting of demi-, occluded, 

 and in addition scattered isolated plates; pore-pairs multiserial. Four to nine 

 columns of plates in each interambulacral area. . Olujoporus (five species). 



Six to twelve columns of plates in each ambulacral area, consisting of demi-, 

 occluded, and one to four irregular columns of isolated plates in each 

 half-area at the mid-zone; pore-pairs multiserial. Three to eleven columns of 

 plates in each interambulacral area. . . . Mcloncchinm (fourteen species). 

 EE. Test elliptical, obovate, spherical, or subspheroidal. Two to twenty columns of 

 plates in each ambulacral area. Three to thirteen columns of plates in each inter- 

 ambulacral area. Plates imbricate. Primordial interambulacral plates in basi- 

 coronal row. Base of corona not resorbed. Oculars usually all insert, genitals 

 with one to many pores each. Periproct plated with many thick plates. Peri- 

 stome with many rows of ambulacral plates only. Primary spines with perforate 

 tubercles, usually eccentric and irregularly distributed on interambulacral plates, 

 with secondary spines and tubercles, or the latter only. . Family Lepidesthid.ve. 

 Two columns of plates in each ambulacral area. Four to eight columns of plates 

 in each interambulacral area. Plates quite thick, imbricating moderately. 

 Secondary tubercles only. Genital plates as far as known with only one pore 

 each, the only instance known in the Palaeozoic. Resembles Palaeechinus 

 excepting for the imbrication Lepidechinus (four species). 



Two columns of plates in each ambulacral area. Fi\e columns of plates in each 

 interambulacral area. Plates imbricating strongly. Eccentric perforate 

 primary with secondary tubercles on interambulacral plates. Genital plates 

 with many pores PerlscJwdomits (twospecies). 



