672 THE CRINOLDEA CAMERATA OF NORTH AMERICA. 



Platycrinus grapMcus Hall and Whitf. 

 riate LXXI. Fig. 7. 



1863. TTat.t, and Whitfield ; 17tli Rep. N. T. State Cab. Nat. Hist., p. 55 ; and 1875, Geol. Surv. Ohio 



Vol. II., Part II., p. 166, Plate 11, Pig. 2. 

 1881. W. and Sp.; Revision, Part II., p. 72 (Proceed. Acad. Nat. Sci. Pkila., p. 246). 



Syn. P. rkhfieldetisis Hall and Whitf.; 1875, Geol. Sarv. of Ohio, Vol. II., Part II., p. 167, Plate 



11, Pig. 1- 



Below medium size. The known specimens of this species are badly 

 crushed, and it is impossible to give the form and proportions of the calyx, 

 but probably the dorsal cup was moderately short and rounded at the base. 

 The plates are thin and without ornamentation. 



Basal cup apparently deep, its height being probably equal to half the 

 length of the radials. Radials wider than long, subquadrangular, thickened 

 in the middle, the upper faces of the limbs very slightly sloping, and but 

 little excavated for the facet, which faces upwards, and occupies half the 

 width of the plate. Costals rather large, the upper angle sharply pointed, 

 the upper sloping faces distinctly concave. Distichals free from their origin, 

 considerably narrower than the costals, a little longer than wide. Arms four 

 to the ray, rather delicate, the four or five lower joints wedge-form and 

 alternately arranged, the succeeding ones arranged in two series and sub- 

 quadrangular ; all joints moderately long. The pinnules in adult specimens 

 in contact laterally. Structure of ventral disk unknown. Column joints 

 nearly circular, angular around their edges. The column is composed of 

 rather long joints, which alternate with shorter ones, from which we infer 

 that this species possessed internodal joints. 



Horkon and Locality. — Shales of the Waverly group, Richfield, Summit 

 Co., Ohio. 



Type in the New York State Cabinet at Albany. 



Hemar'ks. — The specimen figured by Hall and Whitfield as P. nclifiel- 

 densis undoubtedly represents an immature specimen of P. grajMcus. The 

 authors admit the strong resemblance of the two forms, but separate them 

 upon the arm structure. They described the arms of P. richfieldensis as 

 being " composed of a double series of obtusely wedge-form plates in the 

 lower [upper] part,* the sharp or narrow edges of which extend nearly 



* Tlie description says "lower part," wbicli obviously is meant for upper part, and "upper part" in tbe 

 next line for lower part. 



