51 



Family GLYPTASTERLD^E. 



THYSANOCRINUS MILLIGAN.*:, 11. Sp. 



Pl(tte III, Fig. 23, basal view, the basal plates being in a pit 



and substantially hidden by the column; Fig. 24, azygous 



side; Fig. 25, opposite view. 



Species medium or above medium size. Calyx bowl-shaped, 

 broadly truncated below and slightly expanded above. Pent- 

 agonal in transverse section or as seen from above or below. 

 Plates thick and deeply sculptured. Surface granular. Column 

 small. 



Basals small, deeply sunken in the basal concavity so as to 

 be hidden by the column. Subradials large. They bend into 

 the basal concavity and up on the outside of the calyx, where 

 the height appears to be nearly equal to the width. They 

 terminate below in pyramidal points on which the calyx will 

 rest, if placed on a table, and which extend laterally so as to 

 give a pentagonal outline to the base of the calyx. First 

 primary radials twice as wide as long and bear a subcentral 

 transverse ridge, having raised lines directed to the angular 

 ridges on the subradials below. Second primary radials short, 

 quadrangular, five or six times as wide as long. Third primary 

 radials a little larger than the second, pentagonal, axillary and 

 bear upon each superior sloping side a secondary radial, which 

 gives to this species ten arms. 



There are three regular interradials in each area. The first 

 one rests between the superior sloping sides of the first 

 primary radials and bears a central elongated node. It is 

 followed by two narrow elongated plates that curve over upon 

 the vault. The first azygous plate is large, truncates a sub- 

 radial and bears a large central node. It is followed by three 

 plates, the middle one truncating it slightly. They curve over 

 upon the vault. 



Vault and arms unknown. 



This species is quite different, in form and surface markings, 

 from all other described Thysanocrinus. but it substantially 

 agrees with the generic formula, so far as it is preserved, and 

 we have, therefore, very little doubt about the generic reference. 



Found by Mrs. J. M. Milligan, in whose honor we have pro- 

 posed the specific name, in the Niagara Group, of Decatur 

 County, Tennessee, and now in her collection. 



