CLASS I ECHINOIDEA 303 



Family 3. Palaeechinidae M'Coy. 



Test elliptical, ohovate, spherical or suhspheroidal. Two to twelve columns of 

 plafes in each amhulacral area, ihree to eleven columns of plates in each inter- 

 ambulacral area. Plates not imhricate, hut amhulacral plates hevel over the 

 interambulacral on adradial sutures. Primordial interambulacral plates resorhed. 

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

 usually all insert, genitals usually with three to five pores each. Peristome with 

 many rows of amhulacral and some interradial non-amhulacral plates (Fig. 371, D). 

 Secondary spines and imperforate tuhercles only. Silurian (?), Lower Carboniferous. 



Tliis family includes more species than any other in the Paleozoic. It 

 contains genera with complex ambulacra composed of more than two columns 

 of simple plates in an area, and the species in development pass throngh 

 stages like those of adults in all lower species or genera in the family. The 

 interambulacral plates are very definite in form, and the incoming of columns 

 indicate stages in development. 



Palaeechinus M'Coy (Figs. 367, ^; 430: 431). Two columns of plates in 



Fia. 431. 



Palaeechinus elecjans M'Coy. Lower Carboniferous Limestxjne ; Ireland. A, Test, Vi (after M'Coy). 

 7i, Apical System, more than twice enlarged (after Jackson). 



each amhulacral area, consisting of plates which are all primaries ; pore-pairs 

 uniserial. Four to six columns of plates in each interambulacral area. In 

 this lowest genus the amhulacral detail is like that seen as a developing stage 

 in the higher genera of the family. The test is elliptical, P. quadriserialis^ 

 or nearly spherical, P. elegans. Lower Carboniferous ; Europe and North 

 America. 



Maccoya Pomel (Fig. 367, k). Two columns of plates in each amhulacral 

 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. In this genus, ventrally and dorsally, 

 amhulacral plates as stages in development are all primaries as in Palaeechinus. 

 M. phillipsiae Forbes is attributed to the Silurian (?) of England, other species 

 Lower Carboniferous ; Europe and North America. 



Lovenechinus Jackson (Figs. 367, /; 432). Four columns of plates in each 

 amhulacral area, consisting of demi- and occluded plates ; pore-pairs biserial. 

 Four to seven columns of plates in each interambulacral area. While in this 

 genus there are four columns of amhulacral plates at the mid-zone, primary 

 plates as a stage occur ventrally and dorsally, L. septies. In L. missiouriensis 

 (Jackson) primary with occluded plates exist both ventrally and dorsally as a 



