PLATE 75. 

 Pholidocidaris irregularis Meek and Worthen. Page 434. 



Fig. 1. Keokuk Group, Lower Carboniferous, Keokuk, Iowa. F. Springer Coll., 8,017, young individual. Natural size. 



Six columns of plates in an ambulacral area and six columns of plates in each interambulacral area. The plates 



of the adambulacral columns are relatively very large, especially high; a genital plate occurs in area A (p. 437). 



Drawing, Plate 73, fig. 3. 

 Fig. 2. Keokuk Group, Lower Carboniferous, Montgomery County, Indiana. F. Braun Coll. Another young individual. 



Natural size. Six columns of interambulacral plates in area A, five columns in area C; there are two genital plates 



dorsally (p. 436). Drawing, Plate 73, figs. 4 and 5. 



Figs. 3-5. Keokuk Group. Lower Carboniferous, Hamilton or Nauvoo, Illinois (after Meek and Worthen, 1S73, P late 15, 



figs. 9a, 9b, and 4c. Holotype (p. 436). 



Fig. 3. Portion of dorsal part of a test. Natural size. The orientation is reversed from that given by Meek and Worthen. 

 Ambulacral plates are small. Interambulacral plates imbricate dorsally and from the center laterally and over the 

 ambulacra; in area A there is one adradial column of large, high plates, each bearing an eccentric primary and second- 

 ary tubercles, with three median columns of plates, all much smaller and lower, and bearing secondary tubercles only; 

 the right-hand columns of this area are wanting. In area C there are plates from a right adradial and from median 

 columns, but the plates are displaced and confused. Minute plate-like bodies scattered in the ambulacral anil inter- 

 ambulacral areas are apparently foreign matter. 



Fig. 4. Reverse side of the same specimen. Natural size. The ventral area, showing relatively large ambulacral plates 

 with central pore-pairs, and relatively small interambulacral plates, with primary and secondary spines, all confusedly 

 mixed. 



Fig. 5. One of the primary spines, restored as indicated in outline. X about 2. 



Meekechinus elegans sp. nov. Page. 443. 



Figs. 6-8. Eskridge Shales, at the base of the Permian, Grand Summit, Kansas. J. W. Beede, collector, Univ. of 



Kansas Coll. 



Fig. 6. Holotype. Natural size. The madreporite is in place so that the specimen is oriented by the Loven system. 

 There are 20 columns of low rhombic plates in an ambulacral area at the mid-zone, the highest number known in any 

 sea-urchin. The number of columns in an area is progressively less as we pass dorsally to the apical disc. The 

 interambulacra are narrow, composed in each area of three columns of similar, small, strongly imbricating plates, 

 each typically with one small primary tubercle bounded by a scrobicule, and in addition, rather large secondary 

 tubercles; two or more oculars and five genitals are in place, the latter each with two or more genital pores. The 

 madreporite is very distinct with many fine pores. Drawings, Plate 76, figs. 1-4, and 6. 



Fig. 7. Another specimen, paratype, almost exactly like fig. 1, but not quite as perfectly preserved. Natural size. Par- 

 tially worn away dorsally so that parts of the dorsal portion of eight of the half-pyramids of the lantern are seen. 

 Primary and secondary spines are numerous and well preserved, and in addition, tridentate pedicellariae, the first of 

 such structures known from the Palaeozoic. Drawings, Plate 76, figs. 5, 8, and 9. 



Fig. 8. A fragment of a test, paratype, with well preserved lantern; plates and spines well preserved. Natural size. 

 Drawings, Plate 76, fig. 7. 



