CRETACEOUS FOSSILS. 1 51 



jilaced. in advance of tlie middle; dorsal outline somewhat concave beliind 

 the beaks. Surface apparently smooth. Hinge and interior unknown. 



Length, 0.95 inch; height (of left valve). 0.66 inch. 



I have seen but a single cast of the left valve of this shell (apparently 

 of its exterior), and consequently know nothing of its hinge, muscular, and 

 pallial impressions, nor of the relative convexity of its right valve. It will 

 be seen, however, to agree very closely in form, so far as we have the 

 means of making a comparison, with the large species C. pyriformis, from 

 the fresh- or brackish-water deposits at the Sulphur Creek locality near Bear 

 River, Wyoming, figured on plate 17. The resemblance is so close to cer- 

 tain forms of that variable species, such as fig. 2 « of plate 17, that I should 

 have suspected that the label, indicating a different locality and position, 

 had been accidentally associated with it, were it not for the fact that it is 

 composed of a different material (a light-colored sandstone) from the matrix 

 of the Sulphur Creek fossils. If the label really refers to its proper locality, 

 it will probably prove to be a distinct species from that found at Sulphur 

 Creek, as there seems, so far as yet known, to be no species common to the 

 two localities, unless this one may be so. If a new species, C. pirum would 

 be a good name for it. 



Locality and position. — Coalville, Utah ; Cretaceous sandstone. 



OAEDIID^. 



Genus CARDIUM, Linnaeus. 

 Cardtum curtum, M. & E.l 



Plate 15, fig. 3 (not 3 a). 



Cardium (Semicardiumf) curtum, Meek and Hayden (1861), Proceed. Acad. Nat. Sci. 

 Philad., XIII, 442. 



Shell truncate-suborbicular, with height and length generally about 

 equal, and the gi-eatest convexity along or near the angular posterior umbo- 

 nal slopes; anterior margin rounding into the rounded or semi-ovate base, 

 which is often most prominent slightly behind the middle ; posterior margin 

 obliquely truncated above, and very abruptly rounded or subangular below; 

 beaks elevated, rather pointed, and strongly incurved at right angles to the 

 hinge, placed slightly in advance of the middle; hinge-margin short; posterior 



