COAL MEASURE AND PERMO CARBONIFEROUS FOSSILS. 277 



a little more than twice as long as liigli, with the posterior extremity rounded 

 and recurved; beak large, prominent, and situated at about the anterior 

 third of the length; anterior end rounded, and longest below the middle; 

 basal line slightly convex, more abruptly directed upward for the posterior 

 third of its length; cardinal line concave; valve convex, becoming slightly 

 more compressed posteriorly; marked by slight concentric undulations of 

 growth parallel with the margins. 



Formation and locality. — Upper Coal-Measures (Permo-Carboniferous), 

 foot-hills, southeast of Salt Lake City, Wahsatch Range, Utah. Collected 

 by S. F. Emmons. 



Genus CARDIOMORPHA De Koninck. 

 Cabdiomoepha Missouriensis. 



Plate VI, flss. 1-2. 

 Cardiomorpha Missouriensis Swallow, Trans. Acad. Sci. St. Louis, vol. 1, p. 207, 1858. 



Shell rather below the medium size, transversely elongate and sub- 

 quadrangular in general outline ; valves ventricose, or even gibbous, pre- 

 senting an almost cylindrical form. Hinge-line more than half the length of 

 the shell, very slightly arcuate and abruptly rounding into the posterior 

 extremity, which is obliquely rounded, and longest below; basal margin 

 nearly straight in the middle, curving more abruptly at each extremity; 

 anterior end short, rounded; beaks tumid and enrolled, situated rather 

 within the anterior third of the length ; umbonal prominence faintly sub- 

 angular; cardinal slope nan-ow and abrupt. Surface of the shell marked 

 with fine concentiic stnse of growth and stronger undulations. Substance 

 of the shell very thin. 



The specimens described diflfer so litttle from examples of the species 

 received from the Coal-Measures of Canton, Illinois, that they are not readily 

 distinguished when placed together; the most marked difference being the 

 slightly gi-eater length of the anterior end, and somewhat more prominent 

 beaks. The shell is also a little more excavated in front of the beaks ; but 

 these differences are not strong enough to be deemed of specific importance. 



Formation and localitij. — In black shale of Coal-Measure age, near 

 Eberhardt Mills, White Pine. Collection of Arnold Hague, esq. 



