OF DENISON UNIVERSITY. 65 



Waverly from the Chemung form is futile. Hall states that the pres- 

 ent species differs from S. chemungensis, var. quadrangularis in that 

 the base is more broadly rounded and ihe anterior portion is more ex- 

 panded below, giving the shell a more equilateral appearance. This 

 is not appreciably so in our specimens, though considerable variation 

 is seen. The close relation between the Chemung and Waverly is 

 here obvious. 



Plate IX, Fig. 20 represents a form still more like the (Chemung 

 species. 



Schizodus cicJieus, H. > 



f Plate V, Fig. 15.) 



This little species is not rare in the freestone of middle Waverly, 

 and may be easily recognized by its triangular form and small size. 



Schizodus mediiieiisls, Meek. 



(Plate I, Fig. 16.) 



The figured specimen is imperfect, but characteristic specimens 

 are common in the freestone with the above. 



Ortltoiiota recfi dorsal is. Win. 



(Plate X, F 



&• 



Shell of medium size, elongate, moderately convex. Hinge and 

 ventral margins nearly straight and nearly parallel ; beak sub-terminal ; 

 anterior margin gradually curved to above one half the height, then 

 abruptly curved and slightly concave to the beak, which is very slight- 

 ly elevated. Posterior margin angulate curved, making an angle of 

 about 110° with the hinge line and passing by a more gentle flexture 

 into the ventral border. The greatest thickness is about one-third 

 from the anterior, the surface is evenly convex along a line passing to- 

 ward the postcro ventral angle. There is a rather deep groove pass- 

 ing parallel to the hinge from the beaks. 



