266 ROBERT TRACY JACKSON ON ECHINI. 



*Archaeocidaris agassizi Hall. 

 Plate 13, figs, la-lc, 2-A. 



Archacocidaris agassizi Hall, 1858, p. 698, Plate 26, figs. la-Id; Loven, 1874, p. 43; Quenstedt, 1875, 

 p. 373, Plate 75, fig. 11; Keyes, 1894, p. 127, Plate 15, fig. 5; 1895, p. 185, Plate 18, fig. 5; Beede, 

 1900, p. 48, Plate 8, figs. 6-6e; Klein, 1904, p. 46; Lambert and Thiery, 1910, p. 124. 



Archacocidaris agassizii Jackson, 1896, p. 213. 



A complete test is unknown, but specimens in Mr. F. Springer's collection add a good 

 deal of information to that previously known. The ambulacra are narrow, plates low, bev- 

 eled strongly under the adradials, pore-pairs uniserial. Interambulacrum with four columns of 

 plates in an area; these plates are hexagonal, the height about equal to the width, basal 

 terrace developed; many secondary tubercles are in a narrow row about the margin of plates. 

 Primary spines are elongate, compressed, contracted above the milled ring, swollen in the lower 

 third, and from there tapering to the tip, smooth proximally, above which muricate with small 

 spinulose tubercles arranged quite definitely. 



In Plate 13, fig. 4, are shown some ovally truncate plates which appear to be genitals. As 

 they are not in place, nothing positive can be affirmed, but, while they do not resemble other 

 known genitals in Echini, it is difficult to see what else they could be. The lantern is of the 

 usual character, pyramids wide-angled, with moderately deep foramen, narrow epiphyses, and 

 typical braces. 



Burlington Limestone, Lower Carboniferous, Burlington, Iowa, American Museum of 

 Natural History; Museum of Comparative Zoology Collection 3,034-3,038 and 3,191; F. 

 Springer Collection; University of Michigan; Munich Museum; Hannibal, Missouri (Keyes); 

 Upper Coal Measures, Topeka, Kansas (Beede). 



Archaeocidaris illinoisensis Worthen and Miller. 

 Plate 13, fig. 5. 



Archaeocidaris illinoisensis Worthen and Miller, 1883, p. 338, Plate 31, figs, la, Ib; Keyes, 1895, p. 187; 

 Klem, 1904, p. 49; Lambert and Thiery, 1910, p. 124. 



Known fragmentarily. Primary spines stout, circular, swollen about the middle, studded 

 with short sharp spinules that are directed outward and slightly distally. Rather close to 

 A. agassizi, but the spines are not flattened and spinules are more pronounced as described. 



Beach beds of St. Louis Limestone, Lower Carboniferous, near the Illinois Furnace, Hardin 

 County, Illinois, holotype, no. 2,475, of the Illinois State Collection. 



