504 Observations on the 



referred to P. Burlingto7iensis, of Owen and Shumard, 

 before the discovery of the arms of l)oth species ; but it 

 differs in being constantly much larger, and proportionally 

 higher ; the plates of the dome are more numerous, and 

 differently arranged ; the arms more numerous, and have 

 a different mode of bifurcation. 



Locality ami position, in the upper division of the Bur- 

 lington Limestone, Burlington, Iowa. 



In mi/ own Cabinet, and those of Rev. Mr. Barris and 

 Mr. Wachsmuth. 



Genus CYATHOCRINUS Miller. 



Ct/athocrimis lameUosus (n. s.) Body rather small, sub- 

 globose ; base depressed ; basal plates very small, nearly 

 covered by the last joint of the column ; subradials of 

 medium size, about as high as wide ; first radials about 

 the same size as the subradials, wider than high ; first 

 anal plate, fully half as large as the subradial upon which 

 it rests. The condition of our specimen does not show 

 clearly the number of primary radials to each ray, but they 

 were four, or more in some of the rays. 



Surface marked by high, sharp, radiating ridges, diverg- 

 ing from the centre of each subradial plate to those ad- 

 joining it. These ridges are live in number on each sub- 

 radial, except the one beneath the first anal plate which 

 has six, one of which connects with a perpendicular ridge 

 on the first anal plate, on which plate it is crossed at right 

 angles by a similar ridge. There are two ridges on each 

 first radial plate, which converge at the arm-bases, and are 

 continued in a sharp ridge on the back of each arm and 

 branch, to the ends. The ambulacral grooves along the 

 inner side of the arms and branches, are deep, leaving a 

 thin edge on each side, which, with the sharp ridge on the 

 back, gives a sharp V-shape to a cross section. 



