9 



The vault is exceedingly convex and very slightly depressed in the 

 interradial areas. There is a large tumid plate at the apex of the 

 vault, which is surrounded by seven large tumid plates. There are 

 three large tumid plates over the junction of the ambulacral canals 

 in each of four of the radial series, and one over the junction of the 

 ambulacral canals, in the ray opposite the azygous area. The other 

 plates of the vault are much smaller, but very irregular in size, the 

 smallest ones are in (lie regular interradial and azygous areas. The 

 azygous area is wide and covered by numerous polygonal plates. The 

 azygous orifice is at the superior part of a bulbous swelling and sur- 

 rounded by small plates. 



This is the first sixteen-armed species ever described except the 

 Actinocrinus {?) lielice of Hall to which it bears very little, if any, 

 resemblance. It would seem to be as nearly related to A. iowensis, 

 above described, as to any other species, but it is widely different 

 from that species, in the azygous and interradial areas, in the sec- 

 ondary and tertiary radials, and in the plates of the vault, beside 

 having sixteen arms while that species has only fifteen. It is a very 

 strongly marked species. 



Found in the Keokuk Group, at Keokuk, Iowa, and now in the 

 collection of Wm. F. E. G urley. 



Kemarks on Agaricocrinus. 



Agaricocrinus is a well marked genus that does not graduate into 

 any other nor toward any other through any of the species belong- 

 ing to it. It is only known from the lower half of the Subcar- 

 boniferous System. It first makes its appearance in the Chouteau 

 limestone. Here we find A. hlairi, which has a subquadrate flattened 

 body and bears only nine arms. The ray opposite the azygous area 

 bears a single arm, and each of the other rays bears two. It is the 

 only nine-armed species that has been described, and has very little 

 resemblance in either form or structure to any genus or species that 

 preceded it. There have been described, also, from the Chouteau 

 limestone, three ten-armed species, viz.: A. germanus, which is a 

 small sj)ecies, having a flattened body and a tumid plate above each 

 ambulacral orifice; the vault is covered by fewer plates than any 

 other known species; A. chouteauensis^ which has an abrupt basal 

 depression, subcorneal vault, and unequal radial series; and A. 

 sampsoni, which bears very large arms, in proportion to the size of 



the flattened calyx. These species are widely separated from each 

 —2 



