Klem — Revision of the Palaeozoic Palae'echinoidea. 73 



cate outward. Large saucer shaped depression in the center 

 of each plate. Surface beveled to the margins of the plates. 

 Tubercles smooth, prominent, surrounded by small nodes. 

 Primary spines round, slender, closely striated longitudinally. 



Ambulacra narrow, imbricating adorally. Plates very 

 unequal in size and form and irregularly arranged. Plates 

 pierced by two pores each. 



Geological formation and locality : Lower Burlington Lime- 

 stone, Burlington, Iowa. 



DOUBTFUL GENERA. 



a. DiscocYSTis Gregory 1897.* 

 b. EcHiNODiscus Worthen and Miller 1883. f 



1. ECHINODISCUS KASKASKIENSIS Hall. 



1858. Agelacrinus haskaskiensis . Hall, Geol. Iowa, vol. 1, 



pt. 2, p. 696, pi. 25, ^g. 18. 

 1894. Echinodiscus kaskaskiensis. Keyes, Mo. Geol. Surv. 



vol. 4, p. 133, pi. 18, fig. 3. 

 Geological formation and locality: Kaskaskia Limestone, 

 Kaskaskia, 111. ; Ste. Mary's, Mo. 



2. EcHiNODiscus OPTATUS Worthcn and Miller. 



1883. Echinodiscusoptatus. Worthen and Miller, Geol. Surv. 

 111., vol. 7, p. 336, pi. 31, fig. 9. 

 Geological formation and locality: Chester Limestone, 

 Monroe and Pope Cos., 111. 



3. EcHiNODiscus SAMPSONi Miller. 



1891. Echinodiscus sampsoni. Miller, Adv. Sheets, 17th 

 Rep. Geol. Surv. Ind., p. 76, pi. 12, fig. 6. 



* Quart. Journ. Geol. Soc. Lond., vol. 53, p. 112. 

 t Geol. Surv. 111., vol. 7, p. 335. 



