INVERTEBRATE PALEONTOLOGY. 171 



side.-, 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 easts, 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. (See fig. 14 b.) I at first thought the peculiar 

 projecting point left by what I have supposed might be the scar of the pedal 

 muscle, near the point of each beak of internal casts, might distinguish 

 casts of the form under consideration ; but this is also seen on some of the 

 easts of the Protocardia, which, likewise, has the hinge-teeth very similar, 

 so that the only sure mearfs 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 moulds, the 

 nature of the ornamentation can be very clearly made out. No traces of 

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

 In some respects, it resembles C. Cottaldinum, d'Orbigny (Palaeont. Fr., Ill, 

 pi. 242), from the Neocomian ; but it is rather more coarsely striated, and 

 wants the posterior dorsal impression of that shell, from which it also differs 

 in being less evenly convex. 



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

 ferruginous sandstone of the age of the Dakota group of the Upper Missouri 

 Cretaceous series. 



Genus PROTOCARDIA, Beyrich. 



Synon. — Cardium (sp.), Sowerby, d'Orbigny, and many others; not of Linnaeus. 



Protocardia, Beyrich (1845), Zeitschr. f. Malak., 17.— Geinitz (1846), Gruud. d. Verst, 421.— 



Quensted (1852), Index of Haudb. der Petref., 784.— Conrad (1860), Jour. Acad. Nat. 



Sci. Philad., IV, 278 (as a subgenus of Cardium).— Meek and Hayden (1865), Palaeont. 



Upper Mo., 98.— Roerner (1670), Geol. v. Oberschl., 334.— Conrad (1873), Supp. N. Car. 



Geo]. Rep., 7. 

 Protoeardium, Meek and Hayden (1860), Proceed. Acad. Nat. Sci. Philad., XII, 418 (as a subgenus 



of Cardium).— Gabb (1869); Palaeont. Cal., II, 187 (as a subgenus of Cardium).— 



Stoliczka (1870), Palaeont. Indica, III, 209; and of several earlier and later authors. 

 Pachycardium, Conrad ( 1870), Am. Jour. Couch., V, 96. 



Elym. — rparoc, first ; Kapdia, the lieart. 

 Type. — Cardium Hilluiittm, Sowerby. 



Shell globose, subquadrate, or rarely vertically cordate-suboval, more or 

 less gibbous; valves generally thick, closed behind; surface marked with 

 radiating costse or stria' on the posterior third or fourth, and concentric striae 

 or costse, or sometimes nearly smooth on the sides and front ; free margins 





