552 NORTH AMERICAN INDEX FOSSILS. 



165. G. tuberosus (Lyon and Casseday). Mississippic. 

 Calyx large (one and one half to two inches wide). Tegmen 



flat, with long and branching appendages. Plates tumid. R pro- 

 longed into spines, directed downward. Anus usually covered by 

 Platyceras equilaterum. 



Keokuk of Kentucky, Indiana and Iowa. 



LXI. Glyptocrinus Hall. 

 Calyx obconical to subglobose, often ornamented with radiating 

 striae passing from plate to plate, the elevations following the 

 rays more pronounced, and forming well-defined rounded ridges 

 which meet imperceptably with the free arm plates. B 5. Inter- 

 brachials very numerous and enclosing supplementary anals which 

 sometimes form a continuous series. There are also numerous 

 interdistichals and frequently interpalmars which form conspic- 

 uous depressions between the arm plates. Tegmen low, very 

 slightly extended above the level of the arm bases and composed 

 of minute irregular pieces. Anus excentric, at summit of a small 

 protuberance. Arms 10 to 20, rarely branching beyond the second 

 bifurcation, rising vertically from the calyx, long, slender and 

 uniserial. Column round, or seldom five-sided. Ordovicic. 



166. G. ramulosus BilHngs. Ordovicic. 

 Calyx large (one to two inches wide). Plates unmarked except 



by a conspicuous ridge passing up each ray. Fixed pinnules pass 

 from the second, fourth and fifth plates. Arms long, slender, 

 once-branching. 



Trenton of Ottawa. 



167. G. decadactylus Hall. (Figs. 1882, 1883.) Ordovicic. 

 Arms 20, simple. (Type of genus.) 



Hudson River group of Kentucky and Ohio. 



LXII. Periglyptocrinus Wachsmuth and Springer. 

 Closely allied to Glyptocrinus but with larger B and well- 

 developed biserial arms. Ordovicic. 



168. P. priscus (Billings). Ordovicic. 

 Small (calyx less than one inch wide), obconical. Conspicuous 



ridges pass from the arms down to the center of the R and there 

 divide and continue to the B. Surface pustulose. 

 Black River of Canada. 



