206 PALEONTOLOGY OF ILLINOIS. 



A NEW GENUS FROM THE NIAGARA GROUP OF 

 WESTERN TENNESSEE. 



ALLOCRINUS. (nov. gen.) W. & Spr. 



"A A A. o s another ; H p i v o v a lily. 



AHocrinus belongs to a group of Crinoids which is sparsely 

 represented in America, but of which several genera and a num- 

 ber of species are known to have existed during the Upper 

 Silurian period in Sweden. It belongs to the Camerata, family 

 Melocrinidte, division Stelidiocrinites. Its closest affinities are 

 with Patelliocrinus and Dolatocrinus. It differs, however, from 

 both of them in the form and size of the various calyx plates, 

 in the arm structure, and in the column. The genus is most 

 remarkable for its regularly pentamerous symmetry and 

 uniserial arms. 



Generic diagnosis. Calyx small; the arms very stout. Sym- 

 metry of the dorsal side strictly equilateral. Basals probably 

 three; small; almost completely covered by the column. Primary 

 radials 3x5 ; the first very large ; the other two much smaller, 

 rounded along their outer face so as to appear like arm plates. 

 Secondary radials two or three ; rounded ; quadrangular. Arms 

 strong; uniserial; composed of large transverse plates. Inter- 

 radials two or more, large, deeply impressed between the 

 radials. Column small, round, with a rather small pentangular 

 central canal. 



