5i6 



NORTH AMERICAN INDEX FOSSILS. 



XXVI. Marsipocrinus Bather. (Mar^upiocrinus Phillips.) 

 Resembling Platycrinus, but the lower brachials and first IR 

 entering somewhat more into the dorsal cup; the radial facets 

 nearly straight instead of excavated; the column circular instead 

 of elliptic and the axial canal much larger and pentagonal (Fig. 

 1836). Siluric. 



58. M. tennesseensis (Roemer). (Fig. 1837.) Siluric. 



Width of calyx about twice the height, the latter about equally 



divided between cup and tegmen. Plates thin and flat, usually 



Fig. 1837. Marsipocrinus tennesseensis, hdi^e oi cdXyyi axiA diuaXy SIS. ( After Roemer. ) 



covered with longitudinal and transverse striae meeting at an angle. 

 Niagaran of Tennessee. 



59. M. praematurus (Hall and Whitfield). (Fig. 1838.) Siluric. 

 Plates heavy and strongly convex. Surface smooth. 

 Niagaran of Ohio. 



XXVII. Platycrinus Miller. 

 B 3, large, two of them equal and twice as large as the third, 

 and all closely anchylosed. R long, large, laterally united by close 

 sutures and furnished above with a crescent-shaped articular facet 

 for the brachials, and the limbs with notches for the support of 

 the IR. Succeeding each R is a row of small brachials which 

 divides above the costals into two branches which bifurcate inde- 

 pendently. Plates of the anal interray more numerous than those 



