1881.] NATURAL SCIENCES OF PHILADELPHIA. 265 



Geological Position^ etc. — Pterotocrinus is the last survivor of 

 the PIat3^erinidse, and occurs only in the Kaskaskia limestone of 

 America. 



The following species are known : — 



1879. Pterotocrinus acatas Wetherby. Joum. Cin. Soc. Nat. Hist. (Oct. No.), p. 1, 



PI. 11, figs. 2 a, b, c. Kaskaskia limest. Pulaski Co., Ky. 

 1879. Pterotocr. Mfurcatus Wetherby. Journ. Cin. Soc. Nat. Hist. (Oct. No.), p. 3, 



PI. 11, figs. 1 a, b, c. Kaskaskia limest. Pulaski Co., Ky. 

 1857. Pterotocr. oapitalis Lyon. (Asterocr, capitalis). Type of the genus. Ky. Geol. 



Surv., iii, p. 472, PI. 3, figs. 1 a-k ; Lyon and Cass., 1859, Pterotocr. capitalis, 



Am. Journ. Sci. and Arts, vol. x.xix, p. 68. Kaskaskia limest. Crittenden 



Co., Ky. 

 1860. Pterotocr. Chestereiisis Meek and Worth. Proc. Acad. Nat. Sci. Phila., p. 383; 



and 1866, Geol. Rep. 111. ii, p. 292, PI. 23, figs. 1 a, b, c. Kaskaskia limest. 



Hardin Co., 111. 

 1857. Pterotocr. coronatus Lyon (Asterocr. coronatus). Ky. Geol. Surv , iii, p. 



476, PI. 1, figs. 1, 1 a. Kaskaskia limest. Crittenden Co., Ky. 

 1860. Pterotocr. crassus Meek and Worth. Proc. Acad. Nat. Sci. Phila. p. 382, and 



1866, Geol. Rep. Ill , ii, p. 240, PI. 23, figs. 2 a, b. Kaskaskia limest. Har- 

 din Co., 111. 

 1859. Pterotocr. depressus Lyon and Cass. Am. Journ. Sci. and Arts, vol. xxix. 



p. 68. Kaskaskia limest. Grayson Springs, Ky. 

 *1858. Pterotocr. protaberans Hall. (Dichoor. protuberans). Geol. Rep. Iowa, i, 



Pt. 2, p 689, PI. 25, fig. 7. Kaskaskia limest. Chester, 111. 

 1859. Pterotocr. pyramidalis Lyon and Cass. Am. Joum. Sci. and Arts, xxix, p. 



69. Kaskaskia limest. Grayson and Edmonson Cos., Ky. 

 This species is evidently identical with P. depressus, and was described from 



a specimen showing the vault in place of the arms. 

 1879. Pterotocr. spatulatus Wetherby. Journ. Cin. Soc. Nat. Hist. (Oct. No.), p. 4, 



PI. 11, figs. 3 a, b, c. Kaskaskia limest. Pulaski Co., Ky. 



B. ACTINOCEINIDJE Roemer and Zittel. 



(Amend. Wachsm. and Spr.) 



The name Actinocrinidsfi was first employed b}- Roemer in 1855, 

 who arranged under it Actinocrinus, Amphoracrinus, Dorycrinus 

 and Batocrinus, genera without underbasals, with three basal 

 plates, and in which the first anal piece extends to the line of the 

 first radials. He placed Melocrinus and all genera with four 

 basals and no anal plate within the first radial ring under his 

 Melocrinidjfi, not including, however, Eucalyjjtocrinus nor Cteno- 

 crinus, which latter, as he supposed, had only three basals. 

 Periechocrinus ( Pradocrinus and Saccocrinus), which he thought 

 differed in the anal area, and Ctenocrinus, he placed with Glypto- 

 crinus — of which the underbasals had not been discovered — under 



