304 ROBERT TRACY JACKSON ON ECHINI. 



The Palaechinus gigas M'Coy (Plate 46, figs. 1, 2; Plate 47, fig. 2) is referable to Maccoya 

 (p. 321); but Duncan's (1889, p. 206, fig. 1) Palaeechinus gigas is doubtless based on the 

 specimen in the Museum of Practical Geology which is here referred to Lovenechinus anglicus 

 sp. nov., as shown on p. 346; Plate 46, figs. 5, 6; Plate 47, figs. 3-5. 



The new genus Lovenechinus has four columns of plates in each ambulacral area at the 

 mid-zone, two columns of demi-, and two of occluded in each half-area, but without isolated 

 plates; the pore-pairs are biserial. This genus includes Palaechinus lacazei Julien, Oligoporus 

 mutatus Keyes, 0. nobilis Meek and Worthen, 0. missouriensis Jackson, and the two new 

 species anglicus and septies (p. 326). 



The genus Oligoporus Meek and Worthen is here used in a restricted sense to include species 

 with four columns of ambulacral plates at the mid-zone, two columns of demi-, and two of 

 occluded plates in each half-area, but with, in addition, scattered isolated plates in the middle 

 of each half-area; pore-pairs are multiserial. This is a structural advance on Lovenechinus, 

 and yet not an attainment to the character of Melonechinus. This genus includes Oligoporus 

 blairi Miller and Gurley, 0. coreyi Meek and Worthen, 0. sulcatus Miller and Gurley, 0. 

 halli sp. nov., and 0. danae Meek and Worthen (the type), (p. 351). 



Norwood and Owen's genus Melonites, now called Melonechinus Meek and Worthen, 

 includes species of the family in which at the mid-zone there are from six to twelve columns 

 of plates in each ambulacral area consisting of demi-plates, occluded plates, and one to four 

 more or less irregular columns of isolated plates in each half-area. This genus represents the 

 final stage of differential evolution in the family, and the species are based largely on the number 

 of columns of ambulacral plates which they attain. There has never been any question as to 

 what species should be included in this genus, and it is unnecessary to enumerate them (p. 364). 



Pomel's (1883) genus Xystria was based on Palaechinus (?) konigii, and is here considered 

 under Incertae Sedis (p. 450). 



PALAEECHINUS M'Coy. 



Palaechinus (pars) M'Coy, 1844, p. 171; Pomel, 1883, p. 114; (pars) Lambert and Thiery, 1910, p. 119. 

 Palaeechinus (pars) Loven, 1874, p. 40 (non Palaeechinus Duncan, 1889, p. 204; 1889a, p. 13, see above 



pp. 303, 304). 

 Rhoechinus (pars) Duncan, 1889, p. 205; 1889a, p. 14 (non Rhoechinus Keeping, 1876, for which see 



Lepidechinus, p. 294); (pars) Jackson, 1896, pp. 200, 239; (pars) Tornquist, 1897, p. 754; (pars) 



Klem, 1904, p. 27; (non Rhoechinus, Lambert and Thie"ry, 1910, p. 122). 

 Palechinus Tornquist, 1897, p. 735. 



Test spheroidal or elliptical, ambulacra narrow, with two columns of plates in each area. 

 Ambulacral plates are all primaries alike throughout the area, pore-pairs uniserial. Interam- 

 bulacral areas wide, with from four to six columns of plates in an area at or above the mid- 

 zone, two plates in the basicoronal row in each area. Peristome unknown; oculars insert, 



