PALAEONTOLOGY OF IOWA. 



683 



Fig. 8. View of the antero-lateral and postero-lateral rays of the left side, the latter 

 having the second radial truncate, and sustaining but a single arm. This 

 feature is probably accidental. 



The accompanying diagram illustrates the form and 

 relations of the plates as far as observed. The circular 

 line in this and the following figures indicates the limits 

 of the external concavity of the base. 



Geological position and locality. In the Kaskaskia limestone 

 Illinois. 



Chester, 



Zeacrinus wortheni ( n. s.). 



BODY seraiglobose, concave at the base, the concavity in- 

 volving the subradial and lower part of the first radial plates. 

 Basal plates minute : subradial plates elongate, hexagonal. 

 First radial plates pentagonal, wedgeform and pointed below. 

 Second radial plates pentagonal, wedgeform above, and sup- 

 porting a pair of arms, which are composed of short qua- 

 drangular plates, bifurcating on the fourth plate above the 

 base ; the anterior ray having two quadrangular plates in- 

 serted between the first and last radial, and the arms bi- 

 furcating on the third and fourth plates above the base, some 

 of them bifurcating a second and a third time. 



This species is much larger than the Z. maniformis, and the area of the exterior 

 basal concavity and bifurcation of the arms aro characteristic features. 

 Fio. 111. 



The accompanying diagram, already used in 

 the generic description and remarks, p. 545, is 

 from a specimen of this species. 



