Carboniferous Rocks of the Mississippi Vallei/. 327 



stone, Burlington, Iowa. Collection of Rev. W. H. Ear- 

 ns. 



Codaster Wliitei (n. s.). Body ovoid, a little more ob- 

 tuse above than below, base obtuse ; the length of basal 

 plate, from the central perforation to the top, is equal to 

 the space between the base of the radial and the base 

 of the pseudo-ambulacral areas ; and the distance from 

 the base of the pseudo-ambulacral area to the point of 

 the plate, measuring the sloping face, is a little greater 

 than the preceding measurements. The radial plates are 

 as wide at the base as the length from the base to the 

 pseudo-ambulacral areas, while at the top they are once 

 and a half as wide as at the lower margin ; the entire 

 length, measuring along the suture line to the summit, 

 (interradials not distinguished) is equal to the width at 

 the top of the plate. 



The pseudo-ambulacral fields are narrow and strongly 

 elevated, with a central sulcus, which is quite distinct 

 above, but becomes obsolete towards the lower part; com- 

 posed of a double series of plates on each side, those of the 

 inner range or ambulacral ossicula are smaller than those of 

 the outer ranges. Towards the base the area is contracted, 

 and the inner faces of the outer ranges of plates come in 

 contact; the number of poral pieces in a single inner 

 range is about twenty-three or twenty-four. 



The inter-ambulacral spaces are divided by a sharply 

 defined ridge extending from the apex of the radial plates 

 to the summit ; and between this and the pseudo-ambula- 

 cral field, the surface is marked by strong, rounded strios, 

 separated by deep, narrow grooves, which in the lower 

 part are parallel to the sides of the pseudo-ambulacral field? 

 but in the upper part diverge from this direction, and con- 

 verge to the summit of the central ridge. 



These striated surfaces appear to be composed of sep- 

 arated linear plates, like the pectinated rhombs of Cystid- 



