690 THE CRINOIDEA CAMEEATA OF NORTH AMERICA. 



HoTKon and Locality. — Lower Burlington limestone ; Burlington, Iowa. 



Ty2Je in the (Worthen) Illinois State collection, Springfield. 



Remarks. — This species was described from a poor specimen, in which 

 only the basals and radials were preserved. The markings of the type speci- 

 men are less distinct than in the one we figure, but there can be no doubt 

 that both belong to the same species. The form and ornamentation of the 

 dorsal cup resemble very closely P. lirevinodus Hall, from the Keokuk group, 

 and it is doubtful if the two species are not identical. A satisfactory com- 

 parison cannot be made as long as nothing is known of the structure of the 

 ventral disk of that species, and in this nothing of the arm structure. 



Platycrinus asper M. and W. 

 Plate LXVIII. Figs. 9a, I. 



1861, Meek and Woethen; Proceed. Acad. Nat. Sci. Phila., p. 129; also Geol. Eep. Rliaois, Vol, III., 



p. 468, Plate 18, Fig. 9. 

 1881. W. aud Sp. ; Revisioa, Part 11., p. 70 (Proceed. Acad. Nat. Sci. Pliila., p. Ui). 

 (Not P. asper QaMixiSS, = Storthingocrinus asper). 



Below medium size. Dorsal cup twice as wide as high, gradually spread- 

 ing, the sides nearly straight ; the base depre.ssed, and abruptly and deeply 

 excavated so as to form a narrow, thickened rim with an undulating or rough- 

 ened surface. A similar rugose rim borders the lower and lateral margins 

 of the radials, leaving a small quadrangular depression beneath the facets. 

 Sides of the basi-radial and interradial sutures broadly beveled ; the inter- 

 basal suture lines distinctly grooved. 



Basals rather large, only their outer margins seen in a side view : the 

 excavated inner part considerabl}' wider than the diameter of the column. 

 Radials wider than long, widening moderately upwards, the lower face 

 straight, the outer ends of the upper face slightly sloping ; facet semi, 

 circular, its width equal to half the width of the plate, and .^lightly pro- 

 jecting. Costals subpentangular, the sloping upper faces concave. Distichals 

 once and a half as wide as long, narrower than the costals, and not in con- 

 tact laterally. Palmars nearly as large as the distichals and of the same 

 general form. Arms of medium size, four to six to the ray — six being 

 probably the normal number — composed above the axillaries of sharply 

 cuneate pieces, which gradually turn into biserial; the costals, distichals, 

 and palmars transversely grooved at the middle. Ventral disk high, bulg- 

 ing, composed of rather large, slightly convex pieces ; the ambulacral plates 



