SWALLOW—DESORIPTION OF FOSSILS. 639 
STROPHODONTA QUADRATA, D. §p. 
Shell moderately convex, subquadrangular or semi-ellipti- 
cal, auriculate. Ventral valve highest near t i 
ards the beak, flattened towards the 
margins; ears scarcely defined by an obsolete depression 
which become more obvious when the shell is worn or exfo- 
lated. 
Length, 1, breadth, 1.12; depth of ventral valve, .39. 
This shell may be known by its subquadrate form, surface 
markings, and its gradual slope from the highest part of the 
ventral valve to the beak. 
rom the Hamilton rocks of Callaway county. 
STROPHODONTA ZXQUICOSTATA, 0. SP. 
Shell suborbicular, auriculate, with a sinus on each lateral 
margin anterior to the e 
From the Hamilton Group, in Callaway county: 
Ortuis MissourtENsis, 0. 8p. 
. ; al 
hell small, resupinate, suborbicular, See ay \arpe 
valve convex, flattened and de ressed in front ; ‘ ? 
