OF DENISON UNIVERSITY. 
75 
above the middle. Length 41 mm; height 35 mm. Free-stone of 
upper Waverly. The hinge characters are unknown. 
Microdofi reservatus, Hall. 
(Plate IV, Fig. 14.) 
'fhis species is common in the free-stone of middle Waverly, but 
neither of our figures gives a typical form. Fig. 14 is abnormally ele- 
vated behind. Fig 4 of Plate X, is a small variety with beaks more 
central than usual. See Modiomorpha, below. 
A typical specimen is sub-quadrangular, as long as high, flat, 
and finely marked concentrically. The lower margin is a very shal- 
low elliptical curve ; postero-dorsal slope slightly inclined, nearly plane; 
hinge line behind the beak nearly straight; posterior margin making 
with it an angle of about 120°, very slightly curved, anterior margin 
slightly concave forming an angle of nearly 140° with the hinge, an- 
tero-inferior projection rather abruptly rounded. Hinge in our casts 
showing only a shallow groove before and behind the beak. The 
generic reference is unsatisfactory. 
Grammy sia rhomhoides , Meek. 
(Plate VIII, Fig. 12 ?) 
Typical specimens are frequent in the free-stone of middle Wa- 
verly. (Our figure is from an unusual form which may not repre- 
sent this species. ) 
The relations of the associated form figured on Plate IV, Fig. i, 
are unknown. 
Gammy sia hannihalensis , Shum. 
This species is not very common in the free-stone of middle Wa- 
verly. Certain forms of Palaeoneilo elliptica are are frequently mis- 
taken for it. Fig. 13, of Plate IV, is apparently a fragment of this 
species. 
