24* PROCEEDINGS OF THE ACADEMY OF [1881. 



of them doubtful) being known from the upper part of the Devo- 

 nian. It is found most abundantly in rocks of the Burlington 

 epoch, which embraces the lower portions of the Subcarboniferous, 

 it ceases to exist at the close of the St. Louis limestone. No 

 other genus of the Palaeocrinoidea has so great a number of 

 species, is so abundantly represented, and has so wide a geogra- 

 phical distribution. 



We recognize the following species : — 



1861. Platyorinus aeqaalis Hall. Desc. New Sp. Crin., p. 117; also Geol. Rep. III., 

 V, p. 456, PI. 3, fig. 8. Upper Burlington limestone. Burlington, Iowa. 



1850. PI. americanus Owen and Shumard. Journ. Nat. Sci. Phila. (ser. ii), ii; also 

 1852. U. S. Geol. Rep. Iowa, Wis. and Minn., p. 594, PI. 5 b, figa. 1 a, b. 

 Lower Burlington limestone. Burlington, Iowa. 

 Si/n. PL trunoatus Hall. 1858, Geol. Rep., Iowa, i, pt.ii, p. 537. Hall in this 

 ease described a young specimen of PL amerioanas. The lower part of the 

 arms are composed of s-ingle, wedge-form joints, giving off the pinnules in a 

 zigzag arrangement. 



1861. PL asper Meek and Worthen. (Pleurocrinus) Proc. Acad. Nat. Sci. Phila., 

 p. 129; also 1868, Geol. Rep. 111., iii, p. 468, PI, 18, fig. 9. Upper Burling- 

 ton limestone. Burlington, Iowa. 



1853. PL arenosus DeKoninck and Lehon. Recherch. Crin. Carb. Belg., p. 182, PI. 

 5, fig. 7. Upper part of Mountain limestone. Tournay, Belgium, 



(?) 1838. PL armatus Miinster. Beitr. zur Petref,, vol. i. Mountain limestone (?). 

 Tournay, Belgium (?). 



1853. PL Austinianus De Koninck and Lehon.fi Recherch. Crin. Carb. Belg,, p. 

 169, PL 5, figs. 3 a, b. Mountain limestone. Tournay, Belgium. 

 Syn. PL trigintidactylus Aust. (in part). Mon. Rec, and Foss, Crin., PI. 3, 

 fig. 1 a (not fig. 1 b-g). 



1875. PL bedfordensis Hall. Geol. Surv. Ohio, Pal. ii, p. 161, PI. 13, fig, 4, Erie 

 Shale, Waverly Gr. Bedford, Ohio. 



1879. PL bonoensis White. Proc. Acad. Nat, Sci. Phila., p. 30; also 1880, Hay- 

 den's U. S. Geol. Surv. Invert. Pal., No. 8, p. 160, PI. 40, fig. 5 a. Lower 

 part of Keokuk limestone. Lawrence and Floyd Co,, Ind. 



1861. PL brevinodus Hall, Desc, New Sp, Crin,, p, 4; also Bost. Jour, Nat. Hist 

 p, 286 ; separate photog, plate 2, fig, 5, Keokuk limestone. Keokuk, Iowa. 



1860. PL burlingtonensis Ow, and Sh,f Jour, Acad. Nat. Sci. Phila. (new ser.), 



ii, pt. 1; also 1852, U. S. Geol. Rep. Iowa, Wis, and Minn,, p, 589, PI, 5 a, 



fig. 5. Meek and Worthen, 1873, Geol. Rep. 111., v, p. 452, PI. 3, figs. 6 a. 



b,c. Lower Burlington limestone. Burlington, Iowa. 

 St/n. PL ezsertas Hall. 1858, Geol, Rep, Iowa, i, pt. ii, p, 539. Described 



from a young specimen, 

 .S^yn. PL inornatUS McChesney. 1860, Desc, New Pal. Foss., p. 6; also PL 



barlingtonensis, Chicago Acad. Sci,, i, p. 9, PI, 4, fig. 3. 



1861, PL calycnlus Hall. Desc. New Sp. Crin., p. 16. Burlington limestone. Bur- 



lington, Iowa. Hall's description is too imperfect for identification. 



In species marked f , an anal tube has been observed. 



