PALAEECHINUS. 305 



imperforate, at least externally; genitals wide, high, each with from two to five genital pores; 

 periproct plated with manj^ small angular plates; lantern unknown, but doubtless as in other 

 genera of the family. (See pp. 82, 191.) 



Type species, as selected by Lambert and Thiery (1910, p. 119), P. eUipticus M'Coy, of 

 the Lower Carboniferous of Ireland. 



This genus includes only part of the species referred to it by M'Coy, and the succeeding 

 history is given under discussion of the family. Duncan (1889a, p. 14) referred the genus 

 (which he called Rhoechinus) to his family Archaeocidaridae because there are two columns 

 of ambulacral plates, but in this he showed an entire lack of appreciation of other characters, 

 which unciuestionably associate the genus with the Palaeechinidae not the Archaeocidaridae. 

 Structurally this genus is the most primitive member of the Palaeechinidae because its ambula- 

 crum is like that found in the young, as a developing stage, in the next three genera of the 

 family ; also it is comparable to the young plates seen dorsally as a localized stage in all other 

 genera of the family as set forth diagrammatically in text-figure 237, p. 231. 



Key to the Species of Palaeechinus. ^ 



Four columns of plates in each interambulacral area, test elliptical . P. quadriscrialis Wright, p. 305. 

 Five columns of plates in each interambulacral area, test elliptical . . P. cllipticus M'Coy, p. 307. 

 Five columns of plates in each interambuhicral area, test spheroidal . . P. clegans M'Coy, p. 308. 

 Five or usually six columns of plates in each interambulacral area, test nearly or quite spherical 



P. (?) minor sp. nov., p. 310. 



*Palaeechinus quadriscrialis Wriglit. 

 Text-fig. 217, p. 191; Plate 29, fig. 1; Plate 30, figs. 1-7. 



Pdacchinus quadrlseriaJis Wright, ISfin, pp. 62, 03, and 88, 89, Plate 3, figs, la-lc; Pomel, 1883, p. 114; 



Lambert and Thiery, 1910, p. 119. 

 PalaecUnus eUipticus Baily, 1865a, p. 217; lS65c, p. 65-67, and 88, Plate 3, figs. 2a, 2b; Quenstedt, 1875, 



p. 380, Plate 75, fig. 42; (non Palaeechinus eUipticus Duncan, 1889, see Lovenechinus lacazei this 



memoir, pp. 320, 329, Plate 30, figs. 1, 3). 

 Palaeechinus eUipticus (pars) Loven, 1874, p. 41. 

 Palaeechinus quadriscrialis Loven, 1874, p. 41. 



Rhoechinus quadriscrialis Duncan, 1889, p. 205; Tornquist, 1897, p. 755; Klem, 1904, p. 30. 

 Rhoechinus quadrangularis (by clerical error) Jackson, 1896, table facing p. 242. 



' A number of species which have been referred to the genus Palaeechinus but not known well enough to intercalate in 

 the systematic series, or species of which no description has been published, are taken up later. These are Palaechinus (?) 

 konigii M'Coy, Palaeechinus (?) regnyi nom. nov. ( = P. konincki Julien), Palaechinus robineli Julien, and Rhoechinus sp. 

 (used in the sense of Palaeechinus), considered under Incertae Sedis, p. 450. Also Palaechinus agassizi, P. carpentcri, 

 P. loveni, all of DoUo and Buisseret, considered under Nomina Nuda, p. 457; a.nd Palaechinus sp. Mitchell, considered 

 under Palaeozoic. Forms Incorrectly Referred to Echini, p. 458. 



