PAL^SONOLTOGY OF IOWA. 523 



Cardioiuorpha ? rliomboidea (n. s.). 



SHELL slightly oblique, subrhomboidal, wider than long, 

 moderately convex, somewhat gibbous near the umbo ; beak 

 moderately incurved. 



SURFACE marked by fine radiating striae, and towards the 

 beak, by a few concentric wrinkles. 



The specimen described is a cast, preserving the radiating stria), which are closely 

 similar to those of the preceding species : the concentric wrinkles on the umbo are 

 the only indications of concentric striae. The beak is extended and incurved, as in 

 other species of this genus. 



Geological formation and locality. In Yellow sandstone of the age of 

 the Chemung group : Burlington, Iowa. 



Euoiiiphalus obtusus ( n. s.). 



SHELL discoid, planorbiform. Spire little elevated, con- 

 sisting of five or six volutions which increase in size very 

 gradually from the apex : largest outer volution very ob- 

 tusely angular on the upper side towards the outer margin, 

 and below this somewhat flattened to the periphery of the 

 shell below, where it is very regularly and symmetrically 

 rounded ; upper side, from the obtuse angle to the suture, 

 flat on the inner volutions, and slightly sloping inward on 

 the outer volutions : aperture straight above, circular below. 



SURFACE marked by fine, closely arranged striae of growth. 



This species sometimes attains a diameter of an inch and a half, though usually 

 smaller. It is distinguished from a somewhat similar form in the Burlington lime- 

 stone, by the obtusely angular character of the volutions, the angle being also farther 

 from the periphery; while the upper side is depressed, instead of being elevated to- 

 wards the suture : the volutions are more prominently rounded and the umbilicus 

 deeper, and the striae are more regular and less imbricating than in E. latus. 



Geological formation and locality. In the Oolitic limestone of the age of 

 the Chemung group : Burlington, Iowa. 



