58o NORTH AMERICAN INDEX FOSSILS. 



4. A. wortheni Hall. (Fig. 1915, a-c.) Mississippic. 

 Corona with four columns of interambulacral plates; tubercle of 



plates scarcely separated from annulus which spreads below into a 

 slightly elevated disk; spines slender, smooth or finely granulate, 

 section round. 



St. Louis of Missouri ; Eureka of Nevada. 



5. A. dininnii White. (Fig. 1914.) Carbonic. 

 Spines of several kinds; principal ones fusiform, from 50-60 



mm. long, with greatest diameter near middle, covered with many 

 irregular spinules, projecting at right angles and most abundant 

 on lower part ; smaller spines more slender, equally spinulose. 

 Coal Measures of Nebraska, Iowa and Missouri. 



Fig. 1914. Archaocidaris dininnii^ spine natural size, and base enlarged. 

 (After Hall.) 



6. A. megastylus Shumard. Carbonic. 

 Boss broad and smooth, areolar surface very broad, slightly con- 

 cave exteriorly and surrounded by secondary tubercles ; primary 

 spines robust, long, slender, longitudinally striate, granulose or 

 finely spinulose ; basal ring oblique to axis ; border crenulated. 



Coal Measures of Kansas and Missouri. 



7. A. aculeata Shumard. Carbonic-Permic. 

 Primary tubercles small, but prominent on elevated, smooth boss, 



with deep, circular canal; areola broad, exteriorly marked with 

 obscure striae and secondary tubercles; primary spine, elongate, 

 fusiform, with rather coarse, oblique spinules ; often curved at base 

 and apex. 



Upper Coal Measures of Texas and Missouri ; Permic of Kansas. 



III. Lepidocidaris Meek and Worthen. 

 Differs from Archceocidaris in having additional partial column 

 of ambulacral plates, due to the fact that the individual plates do 

 not always pass across the half area, and up to eight columns of 

 interambulacrals. Mississippic. 



8. L. squamosa Meek and Worthen. (Fig. 191 5, c?.) Mississippic. 

 Ambulacra small, low, often not passing across the half area; 



