1881.] NATURAL SCIENCES OF PHILADELPHIA. 257 



above than below; quadrangular. Interradial plate pushed up- 

 ward to the ventral side of the body, resting upon two upper 

 margins of the first radials, which are not indented ; several inter- 

 radial dome plates follow in succession. 



Dome depressed, and so far as known, constructed, as in some 

 species of Platycrinus, with a short excentric anal tube. 



Column cylindrical, with a small round canal. 



The genus is most closely related to Talarocrinus. 



Geological Position^ etc. — Dichocrinus is a Subcarboniferous 

 genus, and is found in America from the Lower Burlington lime- 

 stone up to the Warsaw, where it is succeeded by Talarocrinus. 

 It is also rejjresented by a number of species in the Mountain 

 limestone of Belgium and Great Britain. 



We recognize the following species : — 



1862. Dichocrinus angustus White. Proc. Bost. Soc. Nat. Hist., ix, p. 19. Upper 



Burlington limest. Burlington, Iowa. 

 1860. Dichocr. constrictus Meek and Worthen. Proc. Acad. Nat. Sci. Phila., p. 



381; also Geol. Rep. 111., ii, p. 263, PI. 19, figs. 2 a, b, c. Warsaw limest. 



Bloomington, Ind. 

 1860. Oichocr. conus Meek and Worthen. Proc. Acad. Nat. Sci. Phila., p. 381 ; 



also Geol Rep. 111., ii, p. 169, PI. 16, figs. 5 a, b. Lower Burlington limest. 



Burlington, Iowa. 

 1862. Dichoor. crassitestus White. Proc. Bost. Soc. Nat. Hist., ix, p. 19. Upper 



Burlington limest. Burlington, Iowa. 

 1860. Dichocr. dichotomus Hall. Supp. Geol. Rep. Iowa, p. 85, PI. 1, fig. 5. War- 

 saw limest. AVarsaw, 111. 

 1853. Dichocr. elegans De Kon. and Leh. (not Casseday and Lyon = Talaro'-rinus 



elegans Wachsm. and Spr.). Rech. Crin. Carb. Belg., p. 153, PI. 4, figs. 13 



a, b. Mountain limest. Tournay, Belg. 

 1836. Dichocr. elongatus (Platycr. elongatus) Phill. (not Goldf., 1838 = Heoca- 



crinns). Geol. of Yorkshire, p. 204, PI. 3, figs. 24, 26; Austin, 1843, Mon. 



Ree. and Foss. Crin. Mount. limest. Tournay, Belg. 

 1853. Dichocr. expansus De Kon. and Leh. (not Meek and Worthen = Dichocr. 



polydactylus Cass, and Lyon). Rech. Crin. Carb. Belg., p. 161, PI. 4, fig. 10. 



Mount, limest. Belgium and England. 

 This species had been figured by Miller, 1821, among his PI. laevis (figs. 4, 5), 



and by Austin as D. radiatus. 

 1860. Dichocr. ficus Casseday and Lyon. Proc. Am. Acad. Arts and So-., v, p. 24 ; 



Meek and Worthen, 1873, Geol. Rep. 111., v, p. 500, PI. 14, fig. 1. Keokuk 



limest. Crawfordsville, Ind. 

 In their description, the above authors state that all of the six perisomic plates 



are arm bearing. This is a mistake, as the anal plate supports a narrow 



cylindrical tube somewhat resembling an arm. 

 1843. Dichocr. fusiformis Austin. Mon. Rec. and Fofs. Crin., p. 47, IM. 5, figs. 6 



a-d; De Kon. and Leh., 1853, Rech. Crin. Carb. Belg., p. 148, PI. 4, fig. 7. 



Mount, limest. Mendip Hills, Eng., and Tournay, Belg. 



18 



