73 



twice as wide as long. Third primary radials a little larger than 

 the second, pentagonal, axillary, and in each ray adjoining the 

 azygous area, bear upon the distal side, two secondary radials, 

 and upon the proximal side, an axillary radial, which bears upon 

 each sloping side a single tertiary radial, which gives to each 

 of these rays three arms. One of the lateral rays is constructed 

 in the same way and bears three arms. In the other lateral ray 

 and in the ray opposite the azygous area, the third primary 

 radials support, upon each upper sloping side, two secondary 

 radials, which gives to each of these rays two arms. There are, 

 therefore, thirteen arms in this species. The arm formula is 

 3+2+2+3+3. 



The azygous and regular interradial areas are all cut off from 

 the vault by the union of the radial plates above them. There is 

 one regular interradial in each area. There are five plates in the 

 azygous area. The first plate is in line with the first primary 

 radials and longer than either of them. It is followed by three 

 plates in the second range, and a smaller intercalated plate to the 

 right of the upper part of the middJe plate. 



The vault is obconoidal, covered with polygonal plates and bears 

 a central proboscis. 



This species has little resemblance to either of the other three 

 thirteen-armed species that have been described from the Burling- 

 ton Group, and need not be compared with any of them. It is 

 quite a peculiar species, and at present we do not know where 

 its nearest relative may be found. 



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

 Missouri, and now in his collection. 



REMARKS ON THE FAMILY ACTINOCRINIM. 



This family prevails above all other crinoids, in the Subcar- 

 boniferous rocks of North America. It first appeared, as now 

 understood, and of course, we can only speak within the limits of 

 the present state of learning, in the Niagara Group of the Upper 

 Silurian, and ended, within the Subcarboniferous. The Upper 

 Silurian genera are Cylicocrinus and Saccocrinus, neither of which 

 are known to occur in the Devonian or Subcarboniferous, though 

 one species, described by Meek and Worthen, as Actinocrinus 

 ampins from the Burlington Group, has been referred to Sacco- 

 —10 



