FOSSILS OF THE BURLINGTON GROUP. 447 



The close similarity of tlie body of some species of this genus and 

 that of another allied form, found in the upper members of the Coal 

 Measures of Nebraska, to the corresponding parts of the genus En- 

 crinus, and their wide difference from all the then known Lower Car- 

 boniferous Crinoids of America, have been appealed to as facts, sustain- 

 ing an opinion maintained by some, that these Nebraska beds belong 

 to the age of the Permian of Europe, instead of the Coal Measures. 

 The fact, however, that we now have the species of this genus described 

 in this paper, from the lower part of the Lower Carboniferous dr Moun- 

 tain Limestone at Burlington, ought, we should think, to be sufficient 

 evidence that no such conclusions can be properly based on this type 

 of fossils. 



EKISOCRIXUS A^TIQUUS, M. and W. 



PI. 2, Fig. 3. 

 Erisocrinus antiquus, MEEK and WOBTHEX. Proceed. Acad. Xat. Sci., Phila., 1869, p. 71. 



BODY small, much depressed, somewhat basin-shaped, 

 or very rapidly expanding from the base to the summit of 

 the first radial pieces, at the connections of which it is very 

 faintly sinuous around the margins as seen from below. 

 Base small, eubpentagonal, almost entirely covered by the 

 round, flat facet for the attachment of the colninn; basal 

 pieces exposing very small pentagonal surfaces three or 

 four times as wide as long. Subradial pieces each about 

 one-half to two-thirds as large as the whole base, all uni- 

 formly pentagonal (there being no visible angle at the mid- 

 dle of the base), and with the upper sloping sides each 

 about twice the length of the lateral margins. First radial 

 pieces about twice as large as the subradials, half as long- 

 as wide, and all equally pentagonal, with the lateral and 

 inferior sloping edges of nearly equal length, and the 

 straight, upper truncated side equaling the entire breadth; 

 articulating upper edge very thick, deeply notched at the mid- 

 dle on the inner edge, and provided with the usual transverse 

 ridge and furrows. Second radials as wide as the first, and 

 about three-fourths as long as wide, angular in the middle 

 on the dorsal side, and constricted on each lateral margin : 



