72 



ORDER ARTHRO POM AT A . 

 Family RHYNCHONBLLIDiE. 



EATONIA COULTERI, n. Sp. 



Plate VII, Fig. 8, ventral view; Fig. 9, dorsal view; Fig. 10, 

 cardinal view; Fig. 11, front view. 



Shell medium size, longitudinally ovoid, fully as wide as long 

 and two-thirds as thick, gradually expanding from the beaks, 

 at first, then more rapidly, and finally broadly rounded at the 

 sides; truncated at the anterior end. Surface marked by fine, 

 radiating, bifurcating striae. 



Ventral valve convex from the middle toward the beak, flat- 

 tened toward the antero-lateral margins and then abruptly in- 

 flected at right angles; extended in a broad, shallow, undefined, 

 mesial depression tow 7 ard the front, where it is also abruptly 

 inflected at right angles. Beak elevated and perforated. Dorsal 

 valve convex in the middle part and sloping in all directions, 

 most rapidly laterally and toward the antero-lateral margins. 

 The central part slopes least toward the anterior margin, and 

 appears as an undefined, elevated, rounded, mesial fold, abruptly 

 inflected at the front- Beak incurved. Margins of the valves 

 denticulated. 



This cannot be mistaken for any other defined species. 



The specific name is given in honor of Frof. John M. Coul- 

 ter, President of Lake Forrest University. 



Found in the Oriskany Group in Jackson County, Illinois, 

 and now in the collection of Wm. F. E. Gurley. 



