INVERTEBRATE PALAEONTOLOGY. IS!) 



In form and general appearance, our C. Owenana resembles this shell 

 very closely, but il has a deeper sinus in the pallial impression, and the sub- 

 stance of its shell is thicker than in the species under consideration. Some 

 varieties of our C. pellucida present, in a side-view, more or less similarity to 

 (his species; but their more compressed form and extreme thinness will 

 prevent them from ever being confounded with it. 



This species was named in honor of our lamented friend, Prof. Chester 

 Dewey, of Rochester University, well known for his zeal in the cause of 

 science and the diffusion of knowledge, as well as through the agency of his 

 own contributions to several departments of science. 



Locality and position. — Moreau River, in the Fox Hills group ; and on 

 the Yellowstone River, in strata containing a blending of the species usually 

 found in the Fox Hills beds and the upper part of the Fort Pierre group. 



Callista (Dosiniopsis) Owcnaiia, M. & H. 



Plate 37, fig. 1. 



Cythcrea Owenana, Meek and Hayden (Nov., 1856), Proceed. Acad. Nat. Sci. Philad.. VIII, 273. 



Meretrix Owenana, Meek and Hayden (May, I860), ib., XII, 185. 



Dione Owenana, Meek (lsiil), Smithsonian Check-List N. Am. Cret. Fossils, 13. 



Shell round-oval, compressed, rather thick; extremities rounded, the 

 anterior side being a little narrower than the other; base forming a regular 

 semi-oval curve, sometimes more prominent before than behind the middle; 

 dorsum declining slightly with a convex outline behind the beaks, rather 

 concave, and sloping more abruptly in front ; beaks moderately elevated, and 

 located in advance of the middle ; muscular impressions shallow, the anterior 

 one being narrow-oval, or subovate, and the posterior broader below and 

 attenuate above; pallial impression provided with an elongate-triangular 

 sinus, which is a little obtuse, or very slightly rounded at the extremity, and 

 extends obliquely forward and upward to a point near the middle of each 

 valve. 



Length, 1.56 inches; height, 1.35 inches; convexity, about 0.66 inch. 



Not having seen the hinge of this species, it is impossible to determine 

 whether or not it really presents the characters of this genus, though its deep 

 angular pallial sinus shows that it cannot be properly retained in the genus 

 Meretrix ( — Cytkerea), as that group is now understood by conchologists. 

 The only specimen 1 have seen retaining any portions of the surface, shows 



