65 



POTERIOCKINUS SAMPSONI, n. sp. 



Plate IV, Fig. 9, azygous side view; Fig. 10, opposite view of 

 same, some of the matrix is attached to the 

 top of the first radials. 



Species medium or below medium size, as indicated by two 

 specimens, one of which is smaller than the one illustrated. 

 Calyx like the frustum of a cone, being broadly truncated be- 

 low, slowly expanding above and having a diameter about one- 

 fourth greater than the height. Surface smooth, possibly, in 

 better preserved specimens, granular. Plates thick and sutures 

 close. Column large, at the superior end, as it entirely covers 

 the truncated end of the calyx. 



Basals moderate size, about a third or a half wider than 

 high. Superior angles distinct though not acute. Subradials 

 the largest plates in the calyx, wider than long, though un- 

 equal in size, three hexagonal, two heptagonal. First radials 

 about twice as wide as long, though slightly unequal in size, 

 and truncated the entire width above, for the reception of the 

 second radials, none of which are preserved, in our specimens. 

 The first azygous plate is smaller than a first radial, nearly 

 equal sided, pentagonal, rests between the superior sloping 

 sides of two subradials and separates the first radial, on the 

 right, from the second azygous plate. The second azygous 

 plate is much smaller than the first, truncates a subradial and 

 separates the first one from the first radial, on the left. The 

 third azygous plate is smaller than the second, as shown by 

 the specimen, which is not illustrated, and beyond it, the 

 plates are not preserved. 



While this species is not distinguished by any very remark- 

 able peculiarities, it is so different from any that have been 

 described from rocks of the same geological age, that no 

 comparison is necessary. 



Found by R. A. Blair, in the Chouteau limestone, at Sedalia, 

 Missouri, and now in the collection of S. A. Miller. The 

 specific name is in honor of F. A. Sampson, a distinguished 

 naturalist of Sedalia. 

 —9 



