306 GEOLOGICAL SURVEY OF THE TERRITORIES. 



they left their imprint in the matrix. It shows the mold of a promi- 

 nent triangular anterior cardinal tooth in front, apparently like that of 

 the last, and behind this there are remains of two prominences, that 

 look like they raigbt be casts of two somewhat diverging cardinal teeth 

 in the right valve, with impressions for two other cardinal teeth in the 

 left ; hence, so far as can be made out, the teeth of the hinge seem to 

 agree with those of the last-described species. Specifically, however, 

 this form differs from the last in its more depressed and transverse out- 

 line, as well as in having its lateral extremities more nearly equal and 

 more narrowly rounded ; the posterior margin not being truncated as 

 in the last. 

 Locality and position : Same as last. Collected by Professor Mudge. 



CARDIUM PAUPERCTTLUM, (MEEK.) 



Shell small, very thin, rather compressed, subovate or subcircular ; 

 beaks moderately prominent and nearly central; surface ornamented 

 by about thirty regular, simple, distinctly defined, radiating costse, 

 which about equal the intermediate furrows, and (owing to the thinness 

 of the valves) are well-defined internally, and thus impart a plicated or 

 crenated character to the margins ; crossing these are numerous very 

 regular, well-defined, delicate marks of growth, that are usually less 

 distinct on the posterior third, but give a neatly crenulated appearance 

 to the costse farther forward. 



The specimens yet seen of this little shell are rarely more than about 

 0.50 inch in diameter, and are all more or less flattened or otherwise 

 distorted. Sometimes they are distorted by antero-posterior pressure, 

 so as to present somewhat the appearance and outline of a Lima, being 

 higher than wide, and more or less oblique; while in other examples 

 they are distorted by vertical pressure, so as to present little or no 

 obliquity, and to show a greater antero-posterior diameter than height. 

 1 have not seen the hinge, but some impressions in the matrix show 

 that it has anterior and posterior lateral teeth like those of Cardium ; 

 it, however, does not belong properly to the typical section of that genus. 



Locality and position : Fort Benton Group, or No. 2 of the Upper 

 Missouri cretaceous series, at the Oil Springs, twenty miles west of Fort 

 Bridger, Wyoming Territory. 



CARDIUM (PROTOCAKDIA) SALINAENSE, (MEEK.) 



Shell small, orbicular-subtrigonal, slightly longer than high, rather 

 gibbous ; pallial margin forming a semicircular curve ; anterior margin 

 rounded, most prominent at or a little above the middle, where it is 

 sometimes inclined to be rather narrowly rounded, while below this it 

 curves off obliquely into the base ; posterior margin broader than the 

 anterior, and faintly subtruncated, or broadly rounded ; beaks moder- 

 ately prominent, convex, and incurved, located slightly in advance of 

 the middle ; dorsal outline sloping more abruptly in front than behind 

 the beak's; surface ornamented on the sides and front by comparatively 

 rather large, rounded, very regular, concentric costse, separated by 

 smaller furrows, and on the posterior side by sixteen to twenty-two 

 smaller radiating costse, that are provided with very regularly-disposed, 

 little, vaulted, scale-like prominences, formed by undulating marks of 

 growth. 



Height, O.GG inch ; length, 0.G8 inch ; convexity, about 0.49 inch. 



This little shell is allied to C. pcrcgrinosum, d'Orbiguy, and O. Hilla- 



