27 



The proboscis is small and central. No ovarian pores can 

 be detected in our specimen, and hence it is probable that they 

 opened through the first plates of the free arms. 



This species is distinguished by its general form, peculiar 

 vault, interradial, azygous and intersecondary areas. Though 

 eighteen species have been heretofore described from the Bur- 

 lington Group, bearing twenty arms, none of them have any 

 near affinity with this species. 



Found by F. A. Sampson, in the Burlington Group, at Se- 

 dalia, Missouri, and now in his collection. 



AMPHORACRINUS SAMPSONI, n. Sp. 



Plate I, Fig. 28, azygous view; Fig. 29, opposite side. 



Species varying from medium to large size. We have a 

 specimen one-half larger than the one illustrated. Calyx bowl- 

 shaped, subpentagonal, about as high as wide. Radial ridges 

 distinct and subangular. Interradial areas very wide between 

 the arms, where they unite with the plates of the vault. Plates 

 depressed convex, but none of our specimens preserve the sur- 

 face ornamentation, if it was ornamented. Column round and 

 small. 



Basals form a shallow hexagonal cup, about two and a half 

 times as wide as the diameter of the column, and bearing a 

 slightly concave depression for the attachment of the column. 

 First primary radials are the largest plates in the calyx; they 

 differ somewhat in size, and each one is about as long as wide, 

 three hexagonal and two heptagonal. Second primay radials 

 differ in size from about one-half to three-fourths as large as 

 the first. They are hexagonal and nearly as long as wide. 

 Third primary radials are much smaller than the second, pen- 

 tagonal, axillary, and support on each superior sloping side 

 two secondary radials, which arrangement gives to this species 

 ten arms. 



There are six regular interradials in each area. The first 

 one is as large as a second primary radial. It is followed by 

 two plates in the second range and three in the third, which 

 unite with the plates of the vault. There is a small plate in 

 each intersecondary radial area that unites with the plates of 

 the vault. The plates in the azygous area are numerous, and 



