180 
IOWA ACADEMY OP SCIENCES. 
echinoderms, the crinoids, exist in myriads, so that the former 
would be expected to be more plentiful in those strata. 
Pholidocidaris irregularis Meek & Worthen. 
Plwlidocidaris irregidaris Meek & Worthen, 1869; Proc. Acad. 
Nat. Sci., Phila., vol. XX, p. 78. 
PliolidocidaTis irregidaris & Worthen, 1873; Geol. Sur. Ill- 
inois, vol. V, p. 512, pi. XV, fig. 9. 
Known material very imperfect; all plates irregular, imbri- 
cating; interambulacral rows six or more; plates with central 
tubercles. 
Horizon and localities. Carboniferous, Keokuk limestone: 
Hamilton and Nauvoo, Illinois. 
PalJechinus burlingtonesis Meek & Worthen. 
Pcdcechinus burUngtonesis Meek & Worthen, 1860; Proc. Acad. 
Nat. Sci., Phila., vol. XI, p. 396. 
Pcdcechinus hurlingtonensis Meek & Worthen, 1860; Geol. Sur. 
Illinois, vol. II, p. 230, pi. xvi, figs. 3a-c. 
Test . spherical, perhaps somewhat depressed at the poles. 
Ambulacra narrow, with a double row of alternately small and 
large plates in each series; poral ossicles about thrice as wide 
as high, five to seven, equaling the height of an adjoining inter- 
ambulacral plate; pores in pairs in a zigzag line. Interambu- 
lacral pieces in four series in each field. Surface marked by 
numerous small tubercles for the attachment of the spines, 
rather regularly arranged in rows of which thirty to forty 
occupy an interambulacral plate. 
Horizon and localities. Lower Carboniferous, Burlington 
limestone: Burlington, Iowa. 
Pal^chinus gracilis Meek & Worthen. 
Pcdcechinus gracilis Meek & Worthen, 1869; Proc. Acad. Nat. 
Sci., Phila., vol. XX, p. 82. 
Pcdcechinus gracilis Meek & Worthen, 1873; Geol. Sur. Illinois, 
vol. V, p. 473, pi. X, fig. 2. 
Similar to P. hurlingtonensis but smaller, ambulacra propor- 
tionately much wider and height of poral pieces greater. Inter- 
ambulacral plates much smaller and arranged in seven or more 
ranges instead of only four. 
Horizon and localities. Lower Carboniferous, Upper Burling- 
ton limestone: Burlington, Iowa. 
