440 ROBERT TRACY JACKSON ON ECHINI. 



Another similar crushed specimen from Keokuk, Iowa, is in Mr. Frank Springer's collec- 

 tion. It is a very large individual (Plate 74, fig. 2) ; the dorsal plates are seen in external view, 

 and, where wanting, part of the ventral plates are seen from the interior and are shaded for 

 contrast. The ambulacral plates are mostly dorsal and therefore small. The adradial plates 

 are large and rounded, as usual, and plates of the median interambulacral columns are smaller. 

 Although fragmentary, it seems that six columns can be made out in each interambulacral area. 

 A lantern in place is strongly inclined with grooved teeth, and the dorsal borders of ten half- 

 pyramids are in place. 



* Pholidocidaris sp. 

 Plate 74, figs. 8-10. 



In a small slab from the Kaskaskia Group, Lower Carboniferous, of Pulaski County, 

 Kentucky, in Mr. Frank Springer's collection, there are a number of small plates referable to 

 Pholidocidaris. They may be young specimens of irregularis, or they may be a distinct species, 

 but there is not enough structure to base any conclusions on. The interest of it is that speci- 

 mens of the genus occur in this locality and horizon. 



The ambulacral plates are typical of those frohi the ventral area in Pholidocidaris and unlike 

 anything known in other genera. Two genital plates are high and wide, with numerous pores. 



* Pholidocidaris tenuis Tornquist. 

 Plate 72, fig. 11; Plate 74, figs. 12, 13. 



Pholidocidaris tenuis Tornquist, 1897, p. 767, Plate 21, figs. 8, 9; Plate 22, fig. 8; Klem, 1904, p. 23; 

 Lambert and Thiery, 1910, p. 123. 



This species was described by Professor Tornquist from numerous interambulacral plates 

 and also primary spines from the Lower Carboniferous of Alsace, Germany. A specimen from 

 the Lower Carboniferous of Lancashire, England, in the Museum of Practical Geology, appears 

 to be referable to this species, and adds something to the known characters and also to the 

 geographical distribution of the species. 



According to Tornquist's description, the interambulacral plates are all of about equal 

 size, 10 mm. in width, irregularly hexagonal, thin, and strongly imbricating. Each plate bears 

 an eccentric large perforate primary tubercle with numerous secondary tubercles (Plate 74, 

 fig. 12). The primary spines are terete, expanded at the base, nearly smooth, but with fine 

 vertical striae which are seen only on considerable magnification. They measure from 10 

 to 15 mm. in length (Plate 74, fig. 13). 



The English specimen consists of a slab 150 nun. long bj' 70 mm. wide, which bears a con- 

 fused mass of dissociated plates, part of which are shown in Plate 72, fig. 11. The interambula- 

 cral plates are thin, scale-like, strongly imbricating. They measure from 8 to 11.5 mm. in 



