554 



NORTH AMERICAN INDEX FOSSILS. 



169. S. nobilis (Hall). (Fig. 1885.) 



Four arm openings to the ray, arranged in pairs. 

 Niagaran of Illinois and Wisconsin. 



Siluric 



Fig. 1885. Siphonocrinus nobilis. Internal mold, with broken base ; and impres- 

 sion from external mold, X Vz- (After Hall, 20th Mus. Rep.) 



LXIV. Macrostylocrinus Hall. 

 Calyx small, obconical to subglobose, generally with prominent 

 ridges along the radial and anal plates. Surface densely covered 

 with very fine striae or small granules. B 3, large and unequal, 

 forming a cup. R very large. Costals two and small, one third 

 the size of the R. Arms 10, long, simple, biserial. Anal inter- 



FiG. 1886. Macrostylocrinus. (After Fig. 1887. Melocrinus. (After Well er.) 



W^eller.) 



radial area distinct, with three plates in first row. Tegmen low. 

 Column round (Fig. 1886). 



Distinguished from related genera by the number of B and by 



