OYSTIDS AND BLASTOIDS. 141 



Orophocrinus stelliformis (Owen & Shumarp). 



Plate xvii, flga. Ua-b. 



Pentremiies stdliformis Owen & Shumard, 1850: Jour. Acad. Nat. Sci., 



Phila., vol. 11, p. 67, pi. vii, figs. 16a-b. 

 Pentremites stdiiformis Owen & Shumard, 1852: U. S. Geol. Sur. Wiscon- 

 sin, Iowa and Minnesota, p. 593, pi. vA, figs. 16a-b. 

 Orophocrinus stelliformis von Seebach, 1864: Nachr. K. Gesellach. Wls- 



sensch., Gottingen, p. 110. 

 Codasler stelliformis rthumard, 1865: Trans. St. Louis Acad. Sci., vol. 



II, p. 359. 

 Codo?iites stelliformis Meek & Worthen, 1869: Proc. Acad. Nat. Sci., 



Phila., p. 84. 

 Codonites stelliformis Meek & Worthen, 1873: Geol. Sur. Illinois, vol. V, 

 p. 146, pi. ix, fig. 5. 



Calyx pentagonal, balloon-shaped, summit depressed, con- 

 vex ; cross-section deeply pentagonal; periphery almost equa- 

 torial ; base narrow, expanding gradually to the basi-radial 

 sutures, and thence rapidly to the radial lips. Basal plates 

 forming a cup which is sometimes considerably wider than 

 high and more or less constricted about its middle; basal su- 

 tures very short. Eadial plates oblong, sides nearly parallel ; 

 bodies concave in the middle; lips much produced ; interra- 

 dial sutures in depressions ; sinuses long and somewhat peta- 

 loid, tapering more or less at their distal ends. Deltoid pieces 

 spearhead-shaped, constricted at about one-third of their 

 length from the proximal ends ; anal deltoid with its distal 

 margin rounded. Ambulacra long and subpetaloid, narrowing 

 rather suddenly at about two-thirds their length from the 

 peristome, raised above the margins of the sinuses ; lancet- 

 plates thick, broadly lanceolate, obtusely keel-shaped in 

 cross-section, and nearly filling the sinuses, scarcely exposed 

 except in the median food-groove; under lancet pieces spatu- 

 late; covering pieces often in a double series and transversely 

 elongated; side plates reaching 50 on each side of the ambu- 

 lacrum, triangular in section and much bent down laterally, 

 but almost meeting in the middle line. Spiracles more or less 

 curved, varying in length from one-third to one-half of the 

 ambulacra, largest at the proximal ends. Five hydrospire 

 folds on each side of the ambulacrum. Mouth very small, the 

 summit plates minute and polygonal. Anus oval, bounded dis- 



