GEOLOGICAL SURVEY OF THE TERRITORIES. 307 



mum, Sowerby. It is much smaller than the latter, however, and has a 

 different outline, not being near so truncated behind, nor so regularly 

 rounded in front. Its concentric cost* are likewise proportionally much 

 larger and less numerous, while the radiating ribs on its posterior side 

 differ in being provided with the numerous little projections mentioued 

 in the description. In the latter character it agrees more nearly with 

 G. peregrinosum, d'Orbigny. It also differs from the latter, however, in 

 having its concentric costse proportionally much larger and less numer- 

 ous, and the radiating ones straighter and occupying a larger area of 

 the valves, while the anterior margin is less broadly and regularly 

 rounded in outline. 



Locality and position : Twelve miles southwest of Salina, Saline 

 County, Kansas; Dakota Group of cretaceous. Professor Mudge, col- 

 lector. 



CARDIUM KANSASENSE, (MEEK.) 



Shell rather small, oval-suborbicular, being generally slightly higher 

 than the antero-posterior diameter, and rather gibbons, with the greatest 

 convexity usually above the middle; pallial margin rounded, or sub- 

 semicircular in outline, being in most cases more prominent behind the 

 middle ; anterior margin more or less regularly rounded ; posterior out- 

 line rounded, or very faintly subtruncated ; dorsal outline sloping 

 abruptly from the beaks before and behind ; beaks elevated, gibbous, 

 incurved, and subcentral, or a little in advance of the middle, and but 

 slightly oblique ; posterior dorsal slopes somewhat flattened ; surface 

 marked by numerous regular, simple, radiating striae, or small costse, 

 that are sometimes interrupted by marks of growth. Hinge strong, 

 with cardinal and anterior lateral teeth stout ; posterior lateral remote 

 and less prominent. Anterior muscular scar rather deep; posterior 

 shallow. Scar of pedal muscle (?) small, very deep, and situated on the 

 inner anterior side, and near the points of the beaks, almost opposite 

 the cardinal teeth. 



Length, 0.94 inch ; height, 1 inch ; convexity, about 0.63 inch. 



This and the last-described species are the two most common shells 

 found at the locality where they were obtained, and being, like the other 

 fossils with which they are associated, found in the condition of casts, 

 not always showing even traces of the surface markings, it is sometimes 

 difficult to distinguish them. Where any remains of the surface mark- 

 ings can be seen, however, they can be at once distinguished by the con- 

 centric costse on the sides and front of the former, and the radiating 

 costse on the corresponding parts of* that under consideration. The 

 latter seems also to have generally attained a somewhat larger size. 

 The inner margins of both appear, from the casts, to be generally nearly 

 smooth, though some of the casts of the form under consideration show 

 faint traces of what seem to have been crenulations, near the middle of 

 the base. I at first thought the peculiar projecting point left by what 

 I have supposed might be the scar of the pedal mucles, near the point' 

 of each beak of internal casts, might distinguish the form under consid- 

 eration ; but this is also seen on some of the casts of the other species, 

 which, likewise, has the hinge teeth very similar, so that the only sure 

 means of distinguishing them seems to be the surface markings. These 

 markings are sometimes distinctly and sharply impressed in the matrix, 

 and by taking gutta-percha impressions from these molds, the nature 

 of the surface markings can be very clearly made out. No traces of 

 nodes, or projecting points of any kind, exist on. the costse of this 

 species. In some respects it resembles C. Gottaldinum, d'Orbigny (Pal. 



