670 THE CRINOIDEA CAMEEATA OF NORTH AMERICA. 



nence ; tlieir upper angles not truncated, or very slightly, and the superior 

 faces of adjoining limbs forming almost a straight line. Eadial facets 

 rather shallow, facing upwards. Costals short, occupying the full width of 

 the facets, subtrigonal, the upper angle obtuse. Distichals and palmars as 

 long as the costals, and fully once and a half as wide as long ; the lower 

 plates of the same ray suturally connected. Arms six to the ray, exception- 

 ally two or four in one of the subdivisions; they are long, cylindrical, and 

 but slightly tapering. Arm plates placed obliquely, sloping to the sides, the 

 lines of union somewhat waving. Pinnules closely packed. The structure 

 of the ventral disk has not been observed, being almost completely covered 

 by the arms in our specimens ; only portions of the middle plate of the first 

 interradial row are visible, which at the four regular sides are marked by 

 a conspicuous, sharply triangular convexity, while at the anal side the con- 

 vexity is quadrangular, and the plate itself bulges outward, indicating the 

 presence of some sort of protrusion in connection with the anus. Stem 

 distinctly elliptic, the two upper joints circular, and smaller than the dia- 

 meter of the basal rim. 



Horizon and Locality. — Kinderhook group ; Le Grand, Marshall Co., 

 Iowa. 



Types in the collection of Wachsmuth and Springer. 



Remarks. — This form was referred by us in 1890 with considerable 

 doubt to P. planus 0. and Sh. More perfect specimens since obtained show 

 that it differs from that species more distinctly than we had supposed, and in 

 redescribing it as a new species we name it in memory of Professor Louis 

 Agassiz. P. jJlanus is a larger species than P. Agassizi, the base is conical in 

 place of rounded, and it has no such rim at the lower end. This rim, which 

 is represented in every specimen, is so conspicuous, and resembles so closely 

 a stem joint, that we were at first inclined to regard it as such, but on grind- 

 ing its surface we discovered plainly the interbasal suture lines. P. planus 

 also has a greater number of arms, the arm joints are longer and about 

 horizontal, while in P. Agassizi they slope at quite an angle outward. It 

 differs from P. Pratteni in the much smaller size of the calyx, and in having 

 proportionally much longer arms. 



