430 PALEONTOLOGY OF ILLINOIS. 



have never seen varieties of a species, in this or any of the allied groups, 

 differing to this extent in such characters, we can but regard the dif- 

 ference as being specific. 



It will be observed that the character of the arm and second radial 

 pieces mentioned as distinguishing this species from Z. ramosus, also 

 occur in the species described in this paper under the name of Z. sco- 

 bina. That species, however, differs from this in having its first radials 

 and subradial plates strongly costate, while its arms are proportionally 

 longer, and differ in being somewhat serrated on each side. It also 

 differs in having two arms, instead of only one, from the anterior ray, 

 as in this, and more divisions in its arms, which divisions are given off 

 at greater intervals. 



Locality and position Burlington group, at Burlington, Iowa. Lower 

 Carboniferous. Mr. WACHSMUTH'S collection. 



ZEACRINUS ASPER, M. and W. 



PI. 1, Fig. 7. 

 Zeacrinus aaper, MEEK and WOKTHEN. Proceed. Acad. Nat. Sci., Phila., 1869, p. 150. 



BODY small, much depressed, or twice and a-half as Avide 

 as high, broadly truncated and concave below, the concavity 

 including the base and about half the length of each sub- 

 radial piece. Base small and nearly or quite hidden by 

 the column. Subradial pieces very abruptly geniculated 

 in the middle, the lower or inner half forming a part of 

 the concavity of the under side, and the upper a part of 

 the outer wall of the body, while their prominent middle 

 forms the margin of the concavity below, each presenting 

 a pentagonal outline, excepting one on the anal side, which 

 is hexagonal. First radial pieces about twice as long as the 

 subradials, and twice as wide as long, all pentagonal in form, 

 with the upper truncated side equaling the full breadth. 

 Second radial pieces as wide, and once and a-half as long 

 as the first, pentagonal in form (unless the anterior one, 

 which has not been seen, may be an exception), and sup- 

 porting the arms on their superior sloping sides, each with 

 a very prominent sharp carina extending up the middle, 

 while the surface on each side of the carina is deeply con- 



