37 



summit. Calyx subhemispherical, base depressed ; sutures dis- 

 tinct; surface oranular. 



Basal plates within the calyx and covered externally by the 

 column. Subradials about as wide as lono,, sharply bending 

 into the columnar cavity and upwaid so as to form a convex 

 rim, for the base of the calyx, and to show full half the length 

 of the plates in a lateral view. First radials about one half 

 wider than long, truncated the entire width above and sepa- 

 rated from the second radials by a gaping suture. Second radi- 

 als of unequal length, some of them longer than the first radials 

 and others shorter, convex longitudinally, constricted on the 

 sides, four of them pentagonal, axillary, and supporting upon 

 each upper sloping side a single arm ; the other one, which is 

 opposite the azygous area, is quadrangular, and has a short 

 upper side and bears a single arm. The species, therefore, has 

 only nine arms. 



The arms are short, comparatively large, very slightly fusi- 

 form and composed of a single series of short plates, that are 

 more or less cuneiform in the middle part of the arms. Each 

 plate bears a pinnule directed upward and inward, which is 

 composed of long joints. 



The first azygous plate is quadrangular, a little longer than 

 wide, placed oblique, the lower end abuts upon a subradial, the 

 under sloping side rests upon another subradial, the opposite 

 side abuts the under .sloping side of the first radial on the 

 right, and the superior side abuts upon the second azygous 

 plate. The second azygous plate is larger than the first, trun- 

 cates a subradial, and occupies almost the entire width of the 

 azygous area. The third azygous plate is quite small and does 

 not seem to extend to the first plate. 



It is quite unnecessary to compare this species with Z. bell- 

 ulus, above described, but it may be compared with the form 

 figured by Hall, as Z. maniformis, which it very much resem- 

 bles. Hall's specimen, however, bears only a slight resemblance 

 to Z. maniformis as figured by Yandall & Shumard, in their 

 contributions to the Geology of Kentucky, and we prefer to 

 compare our species with that which is the true Z. maniformis. 

 Z. maniformis has proportionally a longer and moi-e globose 

 calyx and much longer arms than our species. The second ra- 

 dials in our species are much more constricted on the sides than 



