1(34 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



80 far as they can be made out, they seem to be much as in the existing 

 species of Corbicula, excepting that the anterior cardinal tooth of the lett 

 valve is directed almost horizontally forward instead of obliquely forward and 

 downward; it is also much compressed from above and below, and very 

 prominent, and curved upward. The corresponding tooth of the other valve 

 is much smaller, and overlaps that of the right valve. Behind this prominent 

 anterior cardinal tooth of the left valve, I think I have seen two other diverg- 

 ing and emarginate cardinal teeth, with pits for two corresponding diverging 

 teeth in the right valve. The number and arrangement of the leeth of the 

 hinge woidd, therefore, if correctly understood in the specimen, seem to be 

 almost exactly as in Corbicula, with the exception of the rather more nearly 

 horizontal direction of the anterior cardinal teeth, and the prominence of that 

 of the left valve. 



It is quite possible, how r ever, that if we had specimens showing more 

 clearly the cardinal teeth, we might find differences enough to warrant the 

 establishment of a distinct section allied to Corbicula. 



Locality and position. — Twelve miles southwest of Salina, Kansas ; 

 Dakota Group of the Upper Missouri Cretaceous series. Professor Mudge. 



C o r l> i <• 11 1 a ! siilslrivoiiiiiK. Meek. 

 Plate •-', fig. 6. 

 Corbicula 1 subtrigonalis, Meek (1872), Hayden's Second Geol. Report Survey Territories, 305. 



Shell oval-subtrigonal, about one-fourth longer than wide, rather gibbous 

 the greatest convexity being above the middle; basal outline forming a semi- 

 elliptic curve; extremities rather narrowly and very nearly equally rounded; 

 beaks somewhat depressed and very nearly central ; dorsal outline sloping 

 before and behind the beaks, the latter slope being convex and the former 

 nearly straight. Surface only showing fine lines of growth. Pallial line with 

 a small, obtusely-subangular sinus. 



Length, 1.16 inches; height, 0.90 inch; convexity, about 0.66 inch. 



The only cast of the hinge of this species I have seen is that of a left 

 valve. It shows the impressions of the same elongated and striated lateral 

 teeth seen in the last. The cardinal teeth, however, seem to have unfortu- 

 nately been much injured by maceration or erosion before they left their 

 imprint in the rock. It shows the mould of a prominent triangular anterior 

 cardinal tooth in front, apparently like that of the last, and behind this there 



