62 



somewhat different. In L. suhundata the front half of the superior 

 border is represented as nearly horizontal, and the antei'ior side as 

 broadly rounded ; Avhereas in tbe specimen now under consideration the 

 hinge margin in front is oblique, and the anterior side sub-quadrate. 

 Such a slight variation in outline can scarcely be regarded as of specitic 

 value, but the fossil just described is too imperfect to be satisfactoril}- 

 identified. , 



LuciNA. (?) (Sp. undt.) 

 Probably the adult state of the preceding. 



Fig. 7. 



Compare Lucina occidental^, var. ven/ricosa, Meek and Hayden. "Proceedings of 

 the Academy of Natural Sciences of Philadelphia, 1860," page 427, as L. ventricosa. 

 Also, Meek's " Report on the Cretaceous and Tertiary Fos.sils of the Upper Missouri 

 Country," &c., page 135, Plate XVII., figs. 3, <i, b, c. 



Shell compressed, suborbicular, not at all angular, broadly rounded in 

 front, narrower behind; length rather greater than the height. Beaks 

 small, sub-central or a little in advance of the middle, scarcely raised 

 above the highest level of the hinge margin. Superior border slightly 

 convex and sloping gently downwards posteriorly, more abruptly so 

 towards the anterior end. Ventral margin gibbous in front, contracted 

 behind; posterior extremity narrowly rounded, or perhaps very bluntly 

 pointed about the middle, but apparently not at all truncate. 



The sculpture seems to consist of fine and closely arranged concentric 

 strise, but the surface is much worn. The dentition of the hinge and 

 the other markings on the interior of the valves are unknown. 



The specimen from which the above description was made is much 

 broken at the anterior end, but, judging by the lines of growth, the 

 dimensions are nearly as follows: — Estimated length, thirteen and a 

 half lines; actual height, in the middle, twelve and a half lines; actual 

 thickness, six lines. 



