SYSTEMATIC CLASSIFICATION OF l.< HIM _'li:, 



AA. Two or more columns of simple- plates in each ambulacra! ar.-a, ami ilir.-,- or more mluiniu of plate* 

 in each interambuhuTiil urea (for A, set- p. 201). 



H. Genitals largely covering the dorsal surface. Two columns of low plat.-, in ,-uch ami.ulacral 

 area and three columns of plates in cadi inicraml.iilacral an-a. Platrs n..t imbricate. Prini- 

 ordial interamlmlacral plates in liasicoronal row. Base of eorona n..i resorlx-d. Oculars *mall. 

 strongly exsert by the contact of large genitals. IVriprocl central, structure unknown. iVri- 

 stome central, structure unknown. Lantern and perignathic girdle unknown. 



Order PLKSHX IDAKOII.V 



KB. Genitals small. Two to twenty columns of plates in each amlmlacrul area and three to four- 

 teen columns of plates in each interainlmlacral area. Plates not imbricating, or imbricating; 

 when the latter, ambulacra! plates imbricate ventrally and interambulaeral plates dorsally and 

 from the center laterally and over the ambulacra on the adradial sutures. Primordial ambulacral 

 plates on the peristome. Base of corona resorbed or not. I'eristonir central with many row* of 

 ambulacral plates only, or the same with non-ambulacral plates. I jintcrn inclined, composed of 40 

 pieces, teeth grooved. Foramen magnum moderately deep, epiphytes narrow. No pits in top of 

 pyramids. No perignathic girdle. No peristomal gills. Primary spiue-i and |>erforate tulHTcles 

 with secondary spines and imperforate tubercles, or secondaries only. 



C. Irregular, periproct apparently in nn interambulacrum. Two to four columns of plate* 

 in an ambulacral area, and eight to nine columns of plates in an interambulaeral art-a. Plates 

 thin, imbricating. Oculars and genitals doubtful. . . . Order KCHI.VX 'VSTOIDA. 

 Two columns of plates in an ambulacral area and eight to nine columns of plates in an 

 interambulaeral area. Primordial interainlmlacral plates in basieoronal row. Base of 

 corona not resorbed. Peristome with ambulacral plates only. Ijinteni typically 

 echinoid. Numerous fine spines. (One genus and species.) Family PALAEODUCIDAK. 

 Four columns of plates in an ambulacral area, and eight columns of plates in an interam- 

 bulaeral area. Small primary spines and tubercles. (One genus and species.) 



Family KCIIIMM ^IIDAE. 



CC. Regular, periproct within oculo-genital ring. Two to twenty columns of plates in each 

 ambulacral area, and three to fourteen columns of plates in each interambulaeral are*. 

 Plates imbricate or not. Primordial interainlmlacral plates in basicoronal row, or resorled. 

 Base of corona not resorbed or resorbed. Oculars usually all insert. Genitals typically 

 with more than one pore each; rarely (Lepidechinus) with one pore each. Madreporite 

 usually not recognizable. Periproct covered with many thick plates. Peristome with 

 many rows of ambulacral plates only, or in addition with interradial non-ambulacral plates. 

 Spines primary and secondary, or the latter only. Primary tubercles perforate, secondary 



tubercles imperforate Order PKIUSCHOKt HI NOIDA. 



D. Two columns of plates in each ambulacral area, four to fourteen columns of plates 

 in each interambulaeral area. Plates thin, imbricating. 



E. Four to eight columns of plates in an interambulaeral area. Primordial and 

 additional interambulaeral plates rcsorbed in the advance of |x'ristome. Ocu- 

 lars, genitals, and periproct imperfectly known. Peristome with many rows of 



