284 ROBERT TRACY JACKSON ON ECHINI. 



Family LEPIDOCENTRIDAE Loven. 



Li-pidocentridae (pars) Loven, 1874, p. 39; (pars) Zittel, 1879, p. 482; (pars) Jackson, 1896, p. 241. 

 Archacocidaridae (pars) Loven, 1874, p. 39; (pars) Duncan, 1889a, p. 8; (pars) Jackson, 1896, p. 241. 

 Rhoechinidae (pars) Lambert and Thiery, 1910, p. 121. 



Test spheroidal or flattened horizontally, in the plane of the ambitus circular, pentagonal, 

 or elongate through the axis III, 5. Two columns of plates in an ambulacral area, all primaries, 

 or, in one species, occasional alternate plates slightly occluded. Pore-pairs uniserial, or in one 

 species slightly biserial. Ambulacral plates imbricating adorally and beveled strongly under 

 the adradials. Interambulacra with numerous, 5 to 14, columns of plates in an area, moder- 

 ately thin to very thin. Primordial interambulacral plates are in the basicoronal row; the 

 interambulacra usually have a very accelerated development, additional columns coming in 

 early and rapidly. Interambulacral plates imbricate strongly aborally and from the center 

 outward and over ambulacrals. The peristome is plated with many rows of ambulacral plates 

 only. Oculars are small, insert; genitals wide, low, with many pores as far as known. Peri- 

 proct with many small angular plates. Apical disc small. Lantern inclined, composed of forty 

 pieces. There are five genera, including two new ones. 



KONINCKOCIDARIS Dollo and Buisseret. 



Koninckocidaris Dollo and Buisseret, 1888, p. 959; Duncan, 1889a, p. 9. 

 Perischodomus (pars) Tornquist, 1897, p. 725. 

 Lepidcchinus (pars) Lambert and Thiery, 1910, p. 122. 



Test spheroidal, ambulacra narrow, with two columns of plates in an area. The plates 

 are rather high, and imbricate adorally and strongly bevel under the adambulacrals ; pore-pairs 

 are uniserial. Interambulacra wide, with many (seven to eight) columns of plates in an area; 

 the plates are nearly rhombic in outline, imbricating strongly aborally and from the center 

 laterally and over the ambulacrals. Base of corona, peristome, and lantern unknown. Oculars 

 small, genitals low, plates of periproct as far as known numerous, angular. This genus differs 

 from Lepidocentrus in that the ambulacral plates are relatively high instead of low. Since 

 for ambulacral plates to be high is a primitive character, it is considered a lower genus than 

 Lepidocentrus and one of the two species, K. silurica, is geologically much older than any 

 known Lepidocentrus. 



Type species K. cotteaui Dollo and Buisseret from the Lower Carboniferous of Belgium. 



Key to the Species of Koninckocidaris. 



Ambulacral plates high, two equaling the height of an adambulacral; seven columns of plates in an 

 interambulacral area K. cotteaui Dollo and Buisseret, p. 285. 



Ambulacral plates high, three equaling the height of an adambulacral; eight columns of plates in an 

 interambulacral area. K. silurica sp. nov., p. 285. 



