116 [June, 



Locality. Near Moreau river, in a sand bed, associated with bones of Titano- 

 thcrium? Probably a distant outlier of the White river bone beds. 



Ctrena inteemedea. 



Shell oval-ovate, compressed, rather thin ; estremities'rounded ; base semi- 

 elliptical ; beaks moderately elevated, not gibbous, placed nearly half way from 

 the middle to the anterior end ; surface marked with fine lines of growth, oc- 

 casionally rising into obscui-e concentric wrinkles ; edge of the cardinal border 

 thin ; cardinal teeth close under the beaks, posterior one very oblique. Length 

 76 inch ; breadth -22 inch ; height -68 inch. 



Thisspecies approaches some varieties of C.^M??),of Deshay's(Coq.foss. page 

 ll^,) but is more inequilateral, the posterior end being comparatively longer, 

 the beaks are also less elevated. From the last it will be distinguished by its 

 shorter and more rounded form, more elevated beaks, and much thinner cardinal 

 edge. 



Locality and position. Same as last. 



Cyrena occidentalis. 



Shell sub-triangular, very thick, rather ventricose ; anterior end and base 

 rounded, posterior end sloping abruptly fi'om the beaks, and ventrically sub- 

 truncate at the extremity ; beaks located a little in advance of the middle, and 

 elevated, pointed, incurved, and approximate ; surface marked with strong 

 lines of growth. Length 1 inch; breadth -71 inch; height 1 inch. 



Appears to be intermediate between C cordata of Morris {Proceed. Geol. So- 

 ciety, vol. 10, joZ. Ijfifjs. 7, 8, 9,) and C. antiqua of Ferussac, {see Deshays' Coq. foss., 

 pi. 18, figs. 19,20,21) both of which are Eocene species. From the first, it dif- 

 fers in being relatively higher ; its posterior end is also shorter, and more dis- 

 tinctly subtruncate. From the latter, it differs in being less elevated, not so 

 concave in front of the beaks, nor so regularly arcuate on the posterior slope 

 from the beaks to the base. In front, it presents the same symmetrical cordate 

 outline common to both these species. 



Locality. Bad Lands of the Judith. 



CORBDLA SUBTRIGONALIS. 



Left valve subtrigonal, very convex, obliquely truncate from the beaks to the 

 extremities, the two slopes diverging at an angle of 95''; basal margin rounding 

 up abruptly in front, and converging towards the postei-ior slope at an angle of 

 about 48; beaks elevated, located in advance of the middle ; surface marked by 

 faint lines of growth, and having below the middle three or four concentric 

 wrinkles, which become stronger towards the extremities. The right valve is 

 much more compressed, and without concentric folds. Length -74 inch ; breadth 

 25 inch ; height -55 inch. 



The larger, or left valve of this species, has an obscure ridge passing from the 

 beaks obliquely backwards and downwards to the posterior extremity, along 

 which the valve is abruptly deflected towards the hinge margin. This and the 

 foUowino- species may have possessed other surface markings not now preserved, 

 the specimens being all considerably worn, as if they had been exposed to the 

 action of waves on a beach. 



Locality. Mouth of the Judith, associated with Oslrea svbtrigonalis (Evans and 

 Shumarci), also Melania, raludina, and other fresh water shells. 



CORBULA PERDNDATA. 



PJo-ht valve sub-trigonal, rather compressed, obliquely sub-truncate from the 

 beaks toward both extremities, the slopes diverging at an angle of about 82 ; 

 basal margin rounding up in front, straight towards the posterior ; beaks small, 

 much elevated, and placed a little in advance of the middle; surface ornament- 

 ed by five or six strong, elevated, concentric folds, otherwise apparently smooth. 

 Length ^32 inch; breadth -13 inch; height -27 inch. 



The left valve of this species is yet unknown to us. 



Locality and position. Same as last. 



